The way we currently test with AC_CHECK_DECLS do not work with Clang:
```bash
configure:21492: clang++-10 -std=c++11 -c -g -O2 -DHAVE_BUILD_INFO -D__STDC_FORMAT_MACROS conftest.cpp >&5
conftest.cpp💯10: error: builtin functions must be directly called
(void) __builtin_clz;
^
1 error generated.
```
This also removes the __builtin_clz() check, as we don't actually use
it anywhere, and it's trvial to re-add detection if we do start using
it at some point.
Now that 0.20 branch has been split off, master is 0.20.99 (pre-0.21).
Also clean out release notes.
Tree-SHA512: bba6133ae9708f75206c8934901b9f9909a233330f4dfefb3c24175bf8e11631cdc89a5d24a22421a73083f7eb743e977db8020b87dfbd3c1e6043929a19a285
faf7d4fa86 build: Add cov_fuzz target (MarcoFalke)
fac71e364e build: link fuzz/test_runner.py for out-of-tree builds (MarcoFalke)
faf2c5aca0 build: Remove unused USE_COVERAGE (MarcoFalke)
Pull request description:
Only libFuzzer is supported right now, so clang is required. Thus, this needs a workaround such as https://github.com/bitcoin/bitcoin/issues/12602#issuecomment-562788247
Can be tested with:
```
mkdir build && cd build
../configure --enable-fuzz --with-sanitizers=fuzzer --enable-lcov --enable-lcov-branch-coverage CC=clang CXX=clang++
make $MAKEJOBS
make cov_fuzz
ACKs for top commit:
practicalswift:
ACK faf7d4fa86
Tree-SHA512: 6828f8f81d95f6781713d0b09d7eba2ffdb50217e09ca839db61791a4ed70024859c7a0cb01d9eede79166d574dd57ece01f9d9fe2610d4a72a4ca4a4ce0b838
f7453dcc03 build: remove linking librt for backwards compatibility (fanquake)
Pull request description:
Now that we require glibc 2.17+, see #17538, we can remove linking librt
for backwards compatibility purposes. The `clock_*` functions from librt
were merged into glibc as part of the [2.17 release](https://sourceware.org/ml/libc-announce/2012/msg00001.html):
* The `clock_*` suite of functions (declared in <time.h>) is now available
directly in the main C library. Previously it was necessary to link with
-lrt to use these functions. This change has the effect that a
single-threaded program that uses a function such as `clock_gettime' (and
is not linked with -lrt) will no longer implicitly load the pthreads
library at runtime and so will not suffer the overheads associated with
multi-thread support in other code such as the C++ runtime library.
Note that `librt` is already unused by the RISC-V and AARCH64 binaries as their librts don't export any `clock_*` functions. As an example, you can find a diff of the arm32 vs arm64 librt symbols [here](https://gist.github.com/fanquake/b08cb1f0d14df3133395d7796ebf030c).
Below is the library usage for the `v0.19.0.1` release (can delete these tables pre-merge).
#### RISC-V
```bash
riscv/bin/bitcoin-cli: ['libpthread.so.0', 'libm.so.6', 'libgcc_s.so.1', 'libc.so.6', 'ld-linux-riscv64-lp64d.so.1']
riscv/bin/bitcoin-qt: ['libpthread.so.0', 'libfontconfig.so.1', 'libfreetype.so.6', 'libxcb.so.1', 'libdl.so.2', 'libm.so.6', 'libgcc_s.so.1', 'libc.so.6', 'ld-linux-riscv64-lp64d.so.1', 'libatomic.so.1']
riscv/bin/bitcoin-wallet: ['libpthread.so.0', 'libm.so.6', 'libgcc_s.so.1', 'libc.so.6', 'ld-linux-riscv64-lp64d.so.1', 'libatomic.so.1']
riscv/bin/bitcoind: ['libpthread.so.0', 'libm.so.6', 'libgcc_s.so.1', 'libc.so.6', 'ld-linux-riscv64-lp64d.so.1', 'libatomic.so.1']
riscv/bin/bitcoin-tx: ['libpthread.so.0', 'libm.so.6', 'libgcc_s.so.1', 'libc.so.6', 'ld-linux-riscv64-lp64d.so.1']
riscv/bin/test_bitcoin: ['libpthread.so.0', 'libm.so.6', 'libgcc_s.so.1', 'libc.so.6', 'ld-linux-riscv64-lp64d.so.1', 'libatomic.so.1']
```
#### AARCH64
```bash
aarch64/bin/bitcoin-cli: ['libpthread.so.0', 'libm.so.6', 'libgcc_s.so.1', 'libc.so.6', 'ld-linux-aarch64.so.1']
aarch64/bin/bitcoin-qt: ['libpthread.so.0', 'libfontconfig.so.1', 'libfreetype.so.6', 'libxcb.so.1', 'libdl.so.2', 'libm.so.6', 'libgcc_s.so.1', 'libc.so.6', 'ld-linux-aarch64.so.1']
aarch64/bin/bitcoin-wallet: ['libpthread.so.0', 'libm.so.6', 'libgcc_s.so.1', 'libc.so.6', 'ld-linux-aarch64.so.1']
aarch64/bin/bitcoind: ['libpthread.so.0', 'libm.so.6', 'libgcc_s.so.1', 'libc.so.6', 'ld-linux-aarch64.so.1']
aarch64/bin/bitcoin-tx: ['libpthread.so.0', 'libm.so.6', 'libgcc_s.so.1', 'libc.so.6', 'ld-linux-aarch64.so.1']
aarch64/bin/test_bitcoin: ['libpthread.so.0', 'libm.so.6', 'libgcc_s.so.1', 'libc.so.6', 'ld-linux-aarch64.so.1']
```
#### ARM LINUX GNUEABIHF
```bash
arm32/bin/bitcoin-cli: ['libpthread.so.0', 'librt.so.1', 'libm.so.6', 'libgcc_s.so.1', 'libc.so.6', 'ld-linux-armhf.so.3']
arm32/bin/bitcoin-qt: ['libpthread.so.0', 'librt.so.1', 'libfontconfig.so.1', 'libfreetype.so.6', 'libxcb.so.1', 'libdl.so.2', 'libm.so.6', 'libgcc_s.so.1', 'libc.so.6', 'ld-linux-armhf.so.3']
arm32/bin/bitcoin-wallet: ['libpthread.so.0', 'librt.so.1', 'libm.so.6', 'libgcc_s.so.1', 'libc.so.6', 'ld-linux-armhf.so.3']
arm32/bin/bitcoind: ['libpthread.so.0', 'librt.so.1', 'libm.so.6', 'libgcc_s.so.1', 'libc.so.6', 'ld-linux-armhf.so.3']
arm32/bin/bitcoin-tx: ['libpthread.so.0', 'librt.so.1', 'libm.so.6', 'libgcc_s.so.1', 'libc.so.6', 'ld-linux-armhf.so.3']
arm32/bin/test_bitcoin: ['libpthread.so.0', 'librt.so.1', 'libm.so.6', 'libgcc_s.so.1', 'libc.so.6', 'ld-linux-armhf.so.3']
```
#### LINUX X86_64
```bash
x86_64/bin/bitcoin-cli: ['libpthread.so.0', 'librt.so.1', 'libm.so.6', 'libgcc_s.so.1', 'libc.so.6', 'ld-linux-x86-64.so.2']
x86_64/bin/bitcoin-qt: ['libpthread.so.0', 'librt.so.1', 'libfontconfig.so.1', 'libfreetype.so.6', 'libxcb.so.1', 'libdl.so.2', 'libm.so.6', 'libgcc_s.so.1', 'libc.so.6', 'ld-linux-x86-64.so.2']
x86_64/bin/bitcoin-wallet: ['libpthread.so.0', 'librt.so.1', 'libm.so.6', 'libgcc_s.so.1', 'libc.so.6', 'ld-linux-x86-64.so.2']
x86_64/bin/bitcoind: ['libpthread.so.0', 'librt.so.1', 'libm.so.6', 'libgcc_s.so.1', 'libc.so.6', 'ld-linux-x86-64.so.2']
x86_64/bin/bitcoin-tx: ['libpthread.so.0', 'librt.so.1', 'libm.so.6', 'libgcc_s.so.1', 'libc.so.6', 'ld-linux-x86-64.so.2']
x86_64/bin/test_bitcoin: ['libpthread.so.0', 'librt.so.1', 'libm.so.6', 'libgcc_s.so.1', 'libc.so.6', 'ld-linux-x86-64.so.2']
```
#### LINUX i686
```bash
i686/bin/bitcoin-cli: ['libpthread.so.0', 'librt.so.1', 'libm.so.6', 'libgcc_s.so.1', 'libc.so.6', 'ld-linux.so.2']
i686/bin/bitcoin-qt: ['libpthread.so.0', 'librt.so.1', 'libfontconfig.so.1', 'libfreetype.so.6', 'libxcb.so.1', 'libdl.so.2', 'libm.so.6', 'libgcc_s.so.1', 'libc.so.6', 'ld-linux.so.2']
i686/bin/bitcoin-wallet: ['libpthread.so.0', 'librt.so.1', 'libm.so.6', 'libgcc_s.so.1', 'libc.so.6', 'ld-linux.so.2']
i686/bin/bitcoind: ['libpthread.so.0', 'librt.so.1', 'libm.so.6', 'libgcc_s.so.1', 'libc.so.6', 'ld-linux.so.2']
i686/bin/bitcoin-tx: ['libpthread.so.0', 'librt.so.1', 'libm.so.6', 'libgcc_s.so.1', 'libc.so.6', 'ld-linux.so.2']
i686/bin/test_bitcoin: ['libpthread.so.0', 'librt.so.1', 'libm.so.6', 'libgcc_s.so.1', 'libc.so.6', 'ld-linux.so.2']
```
ACKs for top commit:
laanwj:
ACK f7453dcc03
Tree-SHA512: b418260edcda88583abfa386a592ebfb977d111e8e2ba887a30bf830b0b10dba429b9cfd615fad453ff0bb824225914ccb91433064b158ae1fbb9d20fc0b9937
-BEGIN VERIFY SCRIPT-
s() { contrib/devtools/copyright_header.py insert "$1"; }
s build_msvc/bitcoin_config.h
s build_msvc/msvc-autogen.py
s build_msvc/testconsensus/testconsensus.cpp
s contrib/devtools/circular-dependencies.py
s contrib/devtools/gen-manpages.sh
s contrib/filter-lcov.py
s contrib/gitian-build.py
s contrib/install_db4.sh
s src/crypto/sha256_avx2.cpp
s src/crypto/sha256_sse41.cpp
s src/fs.cpp
s src/qt/test/addressbooktests.cpp
s src/qt/test/addressbooktests.h
s src/qt/test/util.cpp
s src/qt/test/util.h
s src/qt/test/wallettests.cpp
s src/qt/test/wallettests.h
s src/test/blockchain_tests.cpp
s test/functional/combine_logs.py
s test/lint/lint-locale-dependence.sh
sed -i '1G' test/lint/lint-shebang.sh
s test/lint/lint-shebang.sh
-END VERIFY SCRIPT-
Now that we require glibc 2.17+, #17538, we can remove linking in librt
for backwards compatibility purposes. The clock_* functions from librt
were merged into glibc as part of the 2.17 release.
* The `clock_*' suite of functions (declared in <time.h>) is now available
directly in the main C library. Previously it was necessary to link with
-lrt to use these functions. This change has the effect that a
single-threaded program that uses a function such as `clock_gettime' (and
is not linked with -lrt) will no longer implicitly load the pthreads
library at runtime and so will not suffer the overheads associated with
multi-thread support in other code such as the C++ runtime library.
https://sourceware.org/ml/libc-announce/2012/msg00001.html
Note that librt is already not linked by the RISC-V and AARCH64 binaries.
as per doc/release-process.md.
Note: On branch-off, these same changes should be made on the release branch, with also these additional changes to both files:
- set `CLIENT_VERSION_REVISION` to `0`
- set `CLIENT_VERSION_IS_RELEASE` to `true`
