gprofng: Don't hardcode -Wno-format-truncation/-Wno-switch

Use -Wno-format-truncation and -Wno-switch only if they are supported.

	PR gprof/28969
	* configure.ac (GPROFNG_NO_FORMAT_TRUNCATION_CFLAGS): New
	AC_SUBST for -Wno-format-truncation.
	(GPROFNG_NO_SWITCH_CFLAGS): New AC_SUBST for -Wno-switch.
	* Makefile.in: Regenerate.
	* configure: Likewise.
	* src/Makefile.am (AM_CFLAGS): Replace -Wno-format-truncation
	and -Wno-switch with GPROFNG_NO_FORMAT_TRUNCATION_CFLAGS and
	GPROFNG_NO_SWITCH_CFLAGS.
	* src/Makefile.in: Regenerate.