https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113376
--- Comment #5 from Jonathan Wakely <redi at gcc dot gnu.org> --- I think https://github.com/llvm/llvm-project/commit/3b9a1bb1af90db9472340ef2122d3855eb9ba3fc#r142768040 is the real cause of the problem. They wanted to avoid -Wundef errors, so changed all the macro tests to use #ifdef instead of #if That is what requires a change to how _PSTL_USAGE_WARNINGS is defined. It also caused other problems elsewhere downstream: https://github.com/oneapi-src/oneDPL/issues/1602
