[llvm] [openmp] Remaining work necessary for GCC 15 (PR #157385)

[Michael Kruse via llvm-commits]

Meinersbur wrote:

Your version of libstdc++ is 15.1, mine is 15.2. What makes the difference might be https://github.com/gcc-mirror/gcc/commit/0dbc588acaa27a3a56bc9173bd577e1293f10046, but I think you might have exceptions enabled because in all cases throwing of `bad_variant_access` is protected by `_GLIBCXX_THROW_OR_ABORT`, i.e. the compiler will not see any use of `bad_variant_access` unless exceptions are enabled. Please check.

https://github.com/llvm/llvm-project/pull/157385