[OpenMP] [test] Skip the -mlong-double-80 test on MSVC ABI (#81115)

Within the MSVC ABI, long doubles are the same as regular 64 bit
doubles. This test case, which is compiled with -mlong-double-80, cannot
work when libomp has been compiled without that flag, as
-mlong-double-80 changes the calling convention for the tested
functions.