gas/

	gas/
	* config/tc-mips.c (RELAX_BRANCH_ENCODE): Encode the temporary
	register to use.
	(RELAX_BRANCH_UNCOND): Adjust accordingly.
	(RELAX_BRANCH_LIKELY): Likewise.
	(RELAX_BRANCH_LINK): Likewise.
	(RELAX_BRANCH_TOOFAR): Likewise.
	(RELAX_BRANCH_AT): New macro.
	(append_insn): Encode the temporary register to use in standard
	MIPS branch relaxation.
	(relaxed_branch_length): Update according to changes to
	RELAX_BRANCH_ENCODE.
	(md_convert_frag): Use the encoded register as the temporary.

	gas/testsuite/
	* gas/mips/relax-at.d: New test for branch relaxation with .set
	at.
	* gas/mips/relax.s: Update to support the new test.
	* gas/mips/relax.l: Update accordingly.
	* gas/mips/relax.d: Update for multi-arch invocation.
	* gas/mips/mips.exp: Run the new test.  Adjust to run "relax"
	across all applicable architectures.