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
b6d301f42d