With the recent change not to install libvtv without
--enable-vtable-verify, I noticed that gcc/g++ would still accept
-fvtable-verify without errors, only to emit obscure link-time errors
about missing vtv_*.o (which hadn't been installed in that situation
before) and libvtv.

It seems to me a much better user experience to emit a clear error
message in this case, which is what this patch does.

Bootstrapped without regressions (without and with
--enable-vtable-verify) on i386-pc-solaris2.12 and x86_64-pc-linux-gnu.
Manually tested that I get (or don't get) the expected errors for
-fvtable-verfy=(none|std|preinit].

Ok for mainline?

	Rainer


2016-05-04  Rainer Orth  <ro@CeBiTec.Uni-Bielefeld.DE>

	* configure.ac (enable_vtable_verify): Handle --enable-vtable-verify.
	* configure: Regenerate.
	* config.in: Regenerate.
	* gcc.c (VTABLE_VERIFICATION_SPEC) [!ENABLE_VTABLE_VERIFY]: Error
	on -fvtable-verify.
	* config/sol2.h [!ENABLE_VTABLE_VERIFY] (STARTFILE_VTV_SPEC): Define.
	(ENDFILE_VTV_SPEC): Define.