Correct mips backend implementation to pass initial tests.

* include/lightning/jit_mips.h, lib/jit_mips-cpu.c,
	lib/jit_mips-fpu.c, lib/jit_mips.c: Correct float/double
	argument handling and make the mips backend pass the initial
	test cases.

	* include/lightning.h, ib/jit_print.c, lib/lightning.c:
	Add extra enum values for argument handling functions that
	could not be abstracted to the current codes, that is, when
	float values need to move from/to gpr from/to fpr. It would
	be more tempting to add such primitives, but they would have
	wordsize limitations, and it is not expected to add codes
	with one gpr argument for 64 bit and two for 32 bit.

	* lib/jit_ppc.c: Check _jit->function before calling jit_epilog()
	to avoid a runtime exception.

lib/jit_ppc.c

@@ -564,7 +564,8 @@ _jit_emit(jit_state_t *_jit)
 	jit_int32_t	 patch_offset;
     } undo;
 
-    jit_epilog();
+    if (_jit->function)
+	jit_epilog();
     jit_optimize();
 
     _jit->emit = 1;