Add support for Loongson EXT instructions.

Add support for Loongson EXT instructions.

gcc/
	* config/mips/mips.h (TARGET_CPU_CPP_BUILTINS): Add
	__mips_loongson_ext.
	(MIPS_ASE_LOONGSON_EXT_SPEC): New.
	(BASE_DRIVER_SELF_SPECS): march=loongson3a implies
	-mloongson-ext.
	(ASM_SPEC): Add mloongson-ext and mno-loongson-ext.
	* config/mips/mips.md (mul<mode>3, mul<mode>3_mul3_nohilo,
	<u>div<mode>3, <u>mod<mode>3, prefetch): Use TARGET_LOONGSON_EXT
	instead of TARGET_LOONGSON_3A.
	* config/mips/mips.opt (-mloongson-ext): Add option.
	* gcc/doc/invoke.texi (-mloongson-ext): Document.

gcc/testsuite/
	* gcc.target/mips/mips.exp (mips_option_groups): Add
	-mloongson-ext option.
	(mips-dg-options): Add mips_option_dependency options
	"-mmicromips" vs "-mno-loongson-ext",

From-SVN: r265863