re PR target/14548 (building Ada library incorrectly requires collect2 on mingw)

re PR target/14548 (building Ada library incorrectly requires collect2 on mingw)

	PR target/14548
	* config.host: Set the shell variable host_can_use_collect2.
	Set it to yes by default, and to no for alpha*-dec-*vms*,
	i[34567]86-*-mingw32*, and powerpc-*-beos*.
	* configure.ac: Set and substitute the shell variable collect2.
	Give an error if use_collect2 is yes and host_can_use_collect2 is
	no.
	* Makefile.in (COLLECT2): Rename from USE_COLLECT2.  Change all
	uses.  Initialize to @collect2@.
	(STAGESTUFF): Remove $(USE_COLLECT2).
	* config/alpha/x-vms (USE_COLLECT2): Don't set.
	* config/i386/t-mingw32 (USE_COLLECT2): Likewise.
	* config/rs6000/t-beos (USE_COLLECT2): Likewise.
	* config/pa/t-pa64: Remove commented out USE_COLLECT2.
	* configure: Regenerate.

Co-Authored-By: Nathanael Nerode <neroden@gcc.gnu.org>
From-SVN: r80422