[SPARC] Errata workaround for GRLIB-TN-0011

[SPARC] Errata workaround for GRLIB-TN-0011

This patch provides a workaround for the errata described in GRLIB-TN-0011.

If the workaround is enabled it will:

 * Insert .align 16 before atomic instructions (swap, ldstub, casa).

It is applicable to GR712RC.

2017-11-29  Daniel Cederman  <cederman@gaisler.com>

gcc/
	* config/sparc/sync.md (swapsi): 16-byte align if sparc_fix_gr712rc.
	(atomic_compare_and_swap_leon3_1): Likewise.
	(ldstub): Likewise.

From-SVN: r255235