MIPS/GAS: Use the module level ISA setting for R6 relaxation

MIPS/GAS: Use the module level ISA setting for R6 relaxation

Use the module level ISA setting rather than the last ISA selected with
a `.set' directive in the source file in determination as to whether to
keep PC-relative relocations and then with the original symbol referred,
for the purpose of R6 linker relaxation.

This is so that with e.g. code like this:

	b	foo
	.set	mips32r2
	...

it's the command line options or any `.module' directive that decides
how to encode any relocation for `foo' rather than the presence of `.set
mips32r2'.

	gas/
	* config/tc-mips.c (mips_force_relocation): Use `file_mips_opts'
	rather than `mips_opts' for the R6 ISA check.
	(mips_fix_adjustable): Likewise.
	* testsuite/gas/mips/pcrel-reloc-1.d: New test.
	* testsuite/gas/mips/pcrel-reloc-1-r6.d: New test.
	* testsuite/gas/mips/pcrel-reloc-2.d: New test.
	* testsuite/gas/mips/pcrel-reloc-2-r6.d: New test.
	* testsuite/gas/mips/pcrel-reloc-3.d: New test.
	* testsuite/gas/mips/pcrel-reloc-3-r6.d: New test.
	* testsuite/gas/mips/pcrel-reloc-1.s: New test source.
	* testsuite/gas/mips/mips.exp: Run the new tests.