libstdc++: Disable test on targets without mkfifo [PR118158]

This test fails to compile using mingw-w64 so disable it using the
dg-require-mkfifo directive.

libstdc++-v3/ChangeLog:

	PR libstdc++/118158
	* testsuite/27_io/filesystem/operations/pr118158.cc: Add
	dg-require-mkfifo.
1 file changed