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

[Michael Kruse via llvm-commits]

https://github.com/Meinersbur commented:

Please add more details on what is happening. Which symbols from libstdc++ is the linker complaining about?

There is a test `no-cpp-dep.c` that should fail if this happens. I works for be with gcc-15, non-optimzed build, shared as well as static flang-rt.runtime. This is what I get with a shared build:
```sh
LD_DEBUG=libs LD_LIBRARY_PATH=/home/meinersbur/src/llvm/work/debug_flangrt/flang-rt/lib ./a.out
     53008:     find library=libflang_rt.runtime.so [0]; searching
     53008:      search path=/home/meinersbur/src/llvm/work/debug_flangrt/flang-rt/lib/glibc-hwcaps/x86-64-v4:/home/meinersbur/src/llvm/work/debug_flangrt/flang-rt/lib/glibc-hwcaps/x86-64-v3:/home/meinersbur/src/llvm/work/debug_flangrt/flang-rt/lib/glibc-hwcaps/x86-64-v2:/home/meinersbur/src/llvm/work/debug_flangrt/flang-rt/lib             (LD_LIBRARY_PATH)
     53008:       trying file=/home/meinersbur/src/llvm/work/debug_flangrt/flang-rt/lib/glibc-hwcaps/x86-64-v4/libflang_rt.runtime.so
     53008:       trying file=/home/meinersbur/src/llvm/work/debug_flangrt/flang-rt/lib/glibc-hwcaps/x86-64-v3/libflang_rt.runtime.so
     53008:       trying file=/home/meinersbur/src/llvm/work/debug_flangrt/flang-rt/lib/glibc-hwcaps/x86-64-v2/libflang_rt.runtime.so
     53008:       trying file=/home/meinersbur/src/llvm/work/debug_flangrt/flang-rt/lib/libflang_rt.runtime.so
     53008:
     53008:     find library=libc.so.6 [0]; searching
     53008:      search path=/home/meinersbur/src/llvm/work/debug_flangrt/flang-rt/lib          (LD_LIBRARY_PATH)
     53008:       trying file=/home/meinersbur/src/llvm/work/debug_flangrt/flang-rt/lib/libc.so.6
     53008:      search cache=/etc/ld.so.cache
     53008:       trying file=/lib/x86_64-linux-gnu/libc.so.6
     53008:
     53008:     find library=libm.so.6 [0]; searching
     53008:      search path=/home/meinersbur/src/llvm/work/debug_flangrt/flang-rt/lib          (LD_LIBRARY_PATH)
     53008:       trying file=/home/meinersbur/src/llvm/work/debug_flangrt/flang-rt/lib/libm.so.6
     53008:      search cache=/etc/ld.so.cache
     53008:       trying file=/lib/x86_64-linux-gnu/libm.so.6
     53008:
     53008:
     53008:     calling init: /lib64/ld-linux-x86-64.so.2
     53008:
     53008:
     53008:     calling init: /lib/x86_64-linux-gnu/libc.so.6
     53008:
     53008:
     53008:     calling init: /lib/x86_64-linux-gnu/libm.so.6
     53008:
     53008:
     53008:     calling init: /home/meinersbur/src/llvm/work/debug_flangrt/flang-rt/lib/libflang_rt.runtime.so
     53008:
     53008:
     53008:     initialize program: ./a.out
     53008:
     53008:
     53008:     transferring control: ./a.out
```
No libstdc++ in sight.

Not being able to create non-optimized builds is what I would consider only as last resort.  Debugging is sometimes necessary to find the cause of bugs.

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