gprof: Compile tst-gmon.c with -O2 -fno-omit-frame-pointer

Compile tst-gmon.c with -O2 -fno-omit-frame-pointer to ensure proper call
graph generation.

	PR gprof/32768
	* configure.ac: Compile tst-gmon.c with -fno-omit-frame-pointer.
	* configure: Regenerated.
	* testsuite/Makefile.am (GPROF_FLAGS): Add -O2
	-fno-omit-frame-pointer.
	(AM_CFLAGS): Removed.
	(COMPILE): Append $(GPROF_FLAGS).
	(LINK): Likewise.
	* testsuite/Makefile.in: Regenerated.

Signed-off-by: H.J. Lu <hjl.tools@gmail.com>