Merge bitcoin/bitcoin#31998: depends: patch around PlacementNew issue in capnp

1ef22ce335 depends: patch around PlacementNew issue in capnp (fanquake)

Pull request description:

  See #31772 and https://github.com/capnproto/capnproto/pull/2235.

  Given there isn't agreement in #29796, pulled this out so it could be merged separately, and it's easier to run different test configurations externally.

  Closes #31772.

ACKs for top commit:
  ryanofsky:
    Code review ACK 1ef22ce335. Confirmed patch is identical to one merged upstream. Only change since last review was tweaking the file paths and commit data in the patch.
  TheCharlatan:
    ACK 1ef22ce335

Tree-SHA512: 9c9ecf50c43cf74315f6659afab55aeafb436f70e83b328016ad574136dce46867220c6e1a85aefd8d3d3d027cd94cc807c79721a4983da9428de70f11224e52

depends/packages/capnp.mk

@@ -4,6 +4,7 @@ $(package)_download_path=$(native_$(package)_download_path)
 $(package)_download_file=$(native_$(package)_download_file)
 $(package)_file_name=$(native_$(package)_file_name)
 $(package)_sha256_hash=$(native_$(package)_sha256_hash)
+$(package)_patches=abi_placement_new.patch
 
 define $(package)_set_vars :=
   $(package)_config_opts := -DBUILD_TESTING=OFF
@@ -12,6 +13,10 @@ define $(package)_set_vars :=
   $(package)_cxxflags += -fdebug-prefix-map=$($(package)_extract_dir)=/usr -fmacro-prefix-map=$($(package)_extract_dir)=/usr
 endef
 
+define $(package)_preprocess_cmds
+  patch -p2 < $($(package)_patch_dir)/abi_placement_new.patch
+endef
+
 define $(package)_config_cmds
   $($(package)_cmake) .
 endef

depends/patches/capnp/abi_placement_new.patch

@@ -0,0 +1,71 @@
+From 74560f26f75dda4257dce541ca362a1e763b2971 Mon Sep 17 00:00:00 2001
+From: Ryan Ofsky <ryan@ofsky.org>
+Date: Thu, 6 Feb 2025 08:39:05 -0500
+Subject: [PATCH 1/1] Avoid gcc/clang ABI incompatibility caused by
+ PlacementNew
+
+GCC and clang do not use same calling convention for passing empty struct
+parameters. There is more information about this in
+https://itanium-cxx-abi.github.io/cxx-abi/cxx-abi-dev/archives/2015-December/002869.html
+
+Unfortunately this can create an issue in capnproto if it is built without
+optimizations in GCC, and the resulting static libraries are used in a clang
+program, or vice versa.
+
+Depending on what order libraries are specified on the linker command line, and
+whether code compiled with the other compiler is calling any header functions
+that cause weak a `operator new(unsigned int, kj::_::PlacementNew, void*)`
+symbol to be defined in its own objects, this can cause the linker to link a
+GCC-generated `kj::ctor` with a clang-generated `operator new`, and the
+resulting program to crash due to the compilers using different calling
+conventions for `operator new`.
+
+This problem is difficult to avoid in general, but pretty easy to avoid here by
+changing `operator new` parameter order so the empty struct parameter is last.
+
+This change should be beneficial for capnproto users that may be compiling it
+without optimizations, and not necessarily using a single compiler to build all
+their dependencies.
+
+The problem does not occur if any optimizations are enabled because `operator
+new` calls are inlined in that case.
+---
+ c++/src/kj/common.h | 11 +++++++----
+ 1 file changed, 7 insertions(+), 4 deletions(-)
+
+diff --git a/c++/src/kj/common.h b/c++/src/kj/common.h
+index b8edde3c..28ab11d6 100644
+--- a/c++/src/kj/common.h
++++ b/c++/src/kj/common.h
+@@ -1034,24 +1034,27 @@ private:
+ 
+ // We want placement new, but we don't want to #include <new>.  operator new cannot be defined in
+ // a namespace, and defining it globally conflicts with the definition in <new>.  So we have to
+-// define a dummy type and an operator new that uses it.
++// define a dummy type and an operator new that uses it.  The dummy type is intentionally passed
++// as the last parameter so clang and GCC ABI calling conventions for empty struct struct parameters
++// are compatible, and there are not segfaults trying to call clang operator new/delete from GCC or
++// vice versa.
+ 
+ namespace _ {  // private
+ struct PlacementNew {};
+ }  // namespace _ (private)
+ } // namespace kj
+ 
+-inline void* operator new(size_t, kj::_::PlacementNew, void* __p) noexcept {
++inline void* operator new(size_t, void* __p, kj::_::PlacementNew) noexcept {
+   return __p;
+ }
+ 
+-inline void operator delete(void*, kj::_::PlacementNew, void* __p) noexcept {}
++inline void operator delete(void*, void* __p, kj::_::PlacementNew) noexcept {}
+ 
+ namespace kj {
+ 
+ template <typename T, typename... Params>
+ inline void ctor(T& location, Params&&... params) {
+-  new (_::PlacementNew(), &location) T(kj::fwd<Params>(params)...);
++  new (&location, _::PlacementNew()) T(kj::fwd<Params>(params)...);
+ }
+ 
+ template <typename T>