Fix and document -r option

Fix and document -r option

The option has existed and been working for years,
make sure it implies the right extra options, and list
it in the documentation.

2018-09-20  Allan Sandfeld Jensen  <allan.jensen@qt.io>

gcc/
	* gcc.c (LINK_COMMAND_SPEC): Handle -r like -nostdlib.
	(VTABLE_VERIFICATION_SPEC): Likewise.
	(SANITIZER_EARLY_SPEC): Likewise.
	(SANITIZER_SPEC): Likewise.
	* config/darwin.h (LINK_COMMAND_SPEC): Likewise.
	* doc/invoke.texi (Link Options): Document -r.

gcc/cp/
	* g++spec.c (lang_specific_driver): Handle -r like -nostdlib.

gcc/fortran/
	* gfortranspec.c (lang_specific_driver): Handle -r like -nostdlib.

gcc/go/
	* gospec.c (lang_specific_driver): Handle -r like -nostdlib.

gcc/testsuite/
	* g++.dg/ipa/pr64059.C: Removed now redundant -nostdlib.
	* g++.dg/lto/20081109-1_0.C: Likewise.
	* g++.dg/lto/20090302_0.C: Likewise.
	* g++.dg/lto/pr45621_0.C: Likewise.
	* g++.dg/lto/pr60567_0.C: Likewise.
	* g++.dg/lto/pr62026.C: Likewise.
	* gcc.dg/lto/pr45736_0.c: Likewise.
	* gcc.dg/lto/pr52634_0.c: Likewise.
	* gfortran.dg/lto/20091016-1_0.f90: Likewise.
	* gfortran.dg/lto/pr79108_0.f90: Likewise.

From-SVN: r264451