testsuite: Only run test on target if VMA == LMA

testsuite: Only run test on target if VMA == LMA

Checking that the triplet matches arm*-*-eabi (or msp430-*-*) is not
enough to know if the execution will enter an endless loop, or if it
will give a meaningful result. As the execution test only work when
VMA and LMA are equal, make sure that this condition is met.

gcc/ChangeLog:

	* doc/sourcebuild.texi: Document new vma_equals_lma effective
	target check.

gcc/testsuite/ChangeLog:

	* lib/target-supports.exp (check_effective_target_vma_equals_lma): New.
	* c-c++-common/torture/attr-noinit-1.c: Requre VMA == LMA to run.
	* c-c++-common/torture/attr-noinit-2.c: Likewise.
	* c-c++-common/torture/attr-noinit-3.c: Likewise.
	* c-c++-common/torture/attr-persistent-1.c: Likewise.
	* c-c++-common/torture/attr-persistent-3.c: Likewise.

Co-Authored-By: Yvan ROUX  <yvan.roux@foss.st.com>
Signed-off-by: Torbjörn SVENSSON  <torbjorn.svensson@foss.st.com>