33796a964a build: Add ability to build qt in depends with -stdlib=libc++ (Hennadii Stepanov)
Pull request description:
This PR makes possible to build the `qt` package in depends against `libc++` for x86_64 platform.
Fixes#22344.
Required for #22815.
Also this PR [fixes](https://github.com/bitcoin/bitcoin/pull/23060#discussion_r716077050) the `[no wallet] [bionic]` task on CI:
- on master (a8bbd4cc81), https://api.cirrus-ci.com/v1/task/5558609250615296/logs/ci.log:
```
Options used to compile and link:
external signer = yes
multiprocess = no
with libs = yes
with wallet = no
with gui / qt = no
```
- this PR, https://api.cirrus-ci.com/v1/task/5502605561430016/logs/ci.log:
```
Options used to compile and link:
external signer = yes
multiprocess = no
with libs = yes
with wallet = no
with gui / qt = yes
```
ACKs for top commit:
fanquake:
ACK 33796a964a - While this sort of string matching is fragile, I think the risk of this causing any actual issues is low.
Tree-SHA512: 586dde2e9864cec7a49aeb4f2b77fb8c4ae96bd10b51f9c6de0cfe8512ad61db15bb7f8d1b0eb6a5a66fd2deee52ac52218f01eb6be107ac12f1a956190de54b
de28c348a0