[MIPS] Fix setjmp signals

Include full 16-byte Mips sigset_t signal mask within jump buffer.
Call sigprocmask instead of sigblockmask/sigsetmask to get/set full signal mask.
Include sigsetjmp's savesigs arg inside jmp_buf, instead of following it.
Reserve room for future extensions.
Preserve historically-large mips32 _JBLEN size.
Eliminate redundancy: code setjmp and _setjmp as tail calls into sigsetjmp,
and make longjmp and _longjmp aliases of siglongjmp.

Change-Id: Ie79137cf059228c1a51344ebb20d3a9a40b4a252
diff --git a/libc/arch-mips/include/machine/setjmp.h b/libc/arch-mips/include/machine/setjmp.h
index a9707dc..4067d51 100644
--- a/libc/arch-mips/include/machine/setjmp.h
+++ b/libc/arch-mips/include/machine/setjmp.h
@@ -6,9 +6,10 @@
 #define _MIPS_SETJMP_H_
 
 #ifdef __LP64__
-#define	_JBLEN	22		/* size, in 8-byte longs, of a mips64 jmp_buf */
+#define	_JBLEN	25	/* size, in 8-byte longs, of a mips64 jmp_buf/sigjmp_buf */
 #else
-#define	_JBLEN	29		/* size, in 4-byte longs, of a mips32 jmp_buf */
+#define	_JBLEN	157	/* historical size, in 4-byte longs, of a mips32 jmp_buf */
+			/* actual used size is 34 */
 #endif
 
 #endif /* !_MIPS_SETJMP_H_ */