libstdc++: Add workaround for ia32 floating atomics miscompilations [PR100184]

libstdc++: Add workaround for ia32 floating atomics miscompilations [PR100184]

gcc on ia32 miscompiles various atomics involving floating point,
unfortunately I'm afraid it is too late to fix that for 11.1 and
as I'm quite lost on it, it might take a while for 12 too
(disabling all the 8 peephole2s would be easiest, but then we'd
run into optimization regressions).

While 1.cc just FAILs, with dejagnu 1.6.1 wait_notify.cc hangs the
make check even after the timeout fires.  The following patch therefore
xfails the former and skips the latter.

Tested on x86_64-linux where
make check RUNTESTFLAGS='conformance.exp=atomic_float/*.cc'
is still
                === libstdc++ Summary ===

 # of expected passes            8
and on i686-linux, where it is now
                === libstdc++ Summary ===

 # of expected passes            5
 # of expected failures          1
 # of unsupported tests          1

2021-04-22  Jakub Jelinek  <jakub@redhat.com>

	PR target/100182
	* testsuite/29_atomics/atomic_float/1.cc: Add dg-xfail-run-if for
	ia32.
	* testsuite/29_atomics/atomic_float/wait_notify.cc: Add dg-skip-if for
	ia32.

(cherry picked from commit 0f4588141fcbe4e0f1fa12776b47200870f6c621)