PR libstdc++/87587 prevent -Wabi warnings

PR libstdc++/87587 prevent -Wabi warnings

The warnings about changes to empty struct parameter passing can be
ignored because the callers are all internal to the library, and so
compiled with the same -fabi-version as the function definitions.

It would be preferable to use #pragma GCC diagnostic warning "-Wabi=12"
to get warnings about any other ABI changes in future versions, but
until PR c++/87611 is fixed the warnings must be completely disabled
with #pragma GCC diagnostic ignroed "-Wabi".

	PR libstdc++/87587
	* src/c++11/cxx11-shim_facets.cc: Suppress -Wabi warnings.

From-SVN: r265163