[Darwin] fix PR67710 by updating 'as' specs to handle newer assembler versions.

[Darwin] fix PR67710 by updating 'as' specs to handle newer assembler versions.

A/ Newer versions of ld64 check the min_version command, and newer versions of
   the system assembler inserts this in response to "-mmacosx-version-min=" on
   the assembler line. Unless one makes sensible versions, some object is bound
   to conflict.

B/ Additionally, there's a difference in behaviour between "as" and "ld" when
   presented with xx.yy.zz (ld truncates to xx.yy, as doesn't); net result is
   that one needs to pass a truncated version to "as".

So (if the assembler supports minversion commands)
(a) provide a truncated minversion (as asm_macosx_version_min, which is a
    driver-only var).
(b) pass this to "as"
(c) Update tests to determine 'HAVE_AS_MMACOSX_VERSION_MIN_OPTION'
    (Rainer's patch)
(d) For some reason the testcases are "run" (it's not obvious they need to be,
    they are checking compile-time issues)
  - anyway, to preserve the status quo, I've left them as exec.  However, the
    minimum version that can be code-gened for is target-dependent (there are no
    released x86 versions before 10.4, for example).  To avoid conflicts where
    the "as" is assuming some minimum, I've set the testversion to 10.5 (which
    is supported by all the archs we have)
(e) We need to ensure that libgcc and crts are generated with a sufficiently
    old minversion not to conflict.

gcc/

2016-11-27  Iain Sandoe  <iain@codesourcery.com>
	    Rainer Orth  <ro@CeBiTec.Uni-Bielefeld.DE>

	PR target/67710
	* config.in: Regenerate
	* config/darwin-driver.c (darwin_driver_init): Emit a version string
	for the assembler.
	* config/darwin.h(ASM_MMACOSX_VERSION_MIN_SPEC): New, new tests.
	* config/darwin.opt(asm_macosx_version_min): New.
	* config/i386/darwin.h: Handle ASM_MMACOSX_VERSION_MIN_SPEC.
	* configure: Regenerate
	* configure.ac: Check for mmacosx-version-min handling.

gcc/testsuite/

2016-11-27  Iain Sandoe  <iain@codesourcery.com>
	    Rainer Orth  <ro@CeBiTec.Uni-Bielefeld.DE>
	    Dominique d'Humieres  <dominiq@lps.ens.fr>

	PR target/67710
	*  gcc.dg/darwin-minversion-1.c: Update min version check.
	*  gcc.dg/darwin-minversion-2.c: Likewise.
	*  gcc.dg/darwin-minversion-3.c: Likewise.

libgcc/

2016-11-27  Iain Sandoe  <iain@codesourcery.com>
	    Rainer Orth  <ro@CeBiTec.Uni-Bielefeld.DE>

	PR target/67710
	*  config/t-darwin: Default builds to 10.5 codegen.

Co-Authored-By: Dominique d'Humieres <dominiq@lps.ens.fr>
Co-Authored-By: Rainer Orth <ro@CeBiTec.Uni-Bielefeld.DE>
From-SVN: r242898