[llvm-branch-commits] dfsan: Fix test with gcc 15. (PR #153873)

[Peter Collingbourne via llvm-branch-commits]

https://github.com/pcc created https://github.com/llvm/llvm-project/pull/153873

With gcc 15 we end up emitting a reference to the
std::__glibcxx_assert_fail function because of this change:
https://github.com/gcc-mirror/gcc/commit/361d230fd7800a7e749aba8ed020f54f5c26d504
combined with assertion checks in the std::atomic implementation.

This reference is undefined with dfsan causing the test to fail. Fix it
by defining the macro that disables assertions.