Disable .gnu.attributes tags in compatibility-ldbl.o

compatibility-ldbl.o is compiled with -mlong-double-64.  When
long double .gnu.attributes tags are checked by the linker, it
complains about the mismatch between this file and others in
libstdc++.

	* configure.ac (LONG_DOUBLE_COMPAT_FLAGS): New ACSUBST.
	* src/Makefile.am (compatibility-ldbl.o, compatibility-ldbl.lo):
	Use LONG_DOUBLE_COMPAT_FLAGS.
	* Makefile.in: Regenerate.
	* configure: Regenerate.
	* doc/Makefile.in: Regenerate.
	* include/Makefile.in: Regenerate.
	* libsupc++/Makefile.in: Regenerate.
	* po/Makefile.in: Regenerate.
	* python/Makefile.in: Regenerate.
	* src/Makefile.in: Regenerate.
	* src/c++11/Makefile.in: Regenerate.
	* src/c++98/Makefile.in: Regenerate.
	* src/filesystem/Makefile.in: Regenerate.
	* testsuite/Makefile.in: Regenerate.

From-SVN: r240602