About the default march and optimizations

[Genuine LoneStar - aka xinzhen]

Buddies:
	Hi, I'm here. Didn't catch you on IRC for days.

	After have a discuss with Zhang Le, I believe the right thing is
march=mips3, with -mfix-loongson2f-nop. This way the produced code can
run on both Loongson 2, and even any other MIPS3 compatible hardware.

	march=loongson2f utilized the 3 additional instructions. As Fai said,
this gives little performance increase, but produces incompatible code.
Not a good idea for now, I think.

	Without -mfix-loongson2f-nop, LS2F may hung. Horrible. XD


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