MIPS: Cleanup the forcing of assembly output in error tests.

MIPS: Cleanup the forcing of assembly output in error tests.

gcc/testsuite

	* gcc.target/mips/oddspreg-2.c (dg-options): Remove dg-skip-if for
	-fno-fat-lto-objects and add the -ffat-lto-objects option, along with
	an explanation for its purpose.
	* gcc.target/mips/oddspreg-3.c (dg-options): Likewise.
	* gcc.target/mips/oddspreg-6.c (dg-options): Likewise.
	* gcc.target/mips/no-dsp-1.c: Add an explanation for the purpose of
	-ffat-lto-objects.
	* gcc.target/mips/pr54240.c: Likewise.
	* gcc.target/mips/r10k-cache-barrier-14.c: Likewise.
	* gcc.target/mips/soft-float-1.c: Likewise.

From-SVN: r243908