Remove -fgnu89-inline configure test.

There is a configure test for -fgnu89-inline.  This option was added
in GCC 4.2, so the test is obsolete; this patch removes it.

Tested for x86_64 (testsuite, and that installed shared libraries are
unchanged by the patch).

	* configure.ac (libc_cv_gnu89_inline): Remove configure test.
	* configure: Regenerated.
	* config.make.in (gnu89-inline-CFLAGS): Remove variable.
	* Makeconfig (CFLAGS): Use -fgnu89-inline instead of
	$(gnu89-inline-CFLAGS).