> build: no longer patch threading out of ld64
>
> Changes introduced in ld64-450.3 have likely removed the need for us to patch out pthreads. See: https://opensource.apple.com/source/ld64/ld64-450.3/src/ld/InputFiles.cpp.auto.html.
> build: use -stdlib++-isystem with Clang 10
This is a partial backport of core#19817
https://github.com/bitcoin/bitcoin/pull/19817/commits/c29cba44b3706e0a2035e440e560f2d15d50433b
https://github.com/bitcoin/bitcoin/pull/19817/commits/b80a6af9e55325d444e117e85bbfc76d88d898a8
https://github.com/bitcoin/bitcoin/pull/19817/commits/a5550f877a2c46d01bb620ae051c0c8ed0fecd0b
Depends on D13777