The issue is that compilation is done with `x86_64-w64-mingw32-g++-posix`,
but then linking is done with `x86_64-w64-mingw32-g++`.
I'm guessing this has been broken since #24131
(01d1845a80), but have not checked.
Fixes#29734.
Unblocks #29527 (now DEBUG=1 builds can be tested).