Correct MIPS types of SA_* flags

[alexcrichton]

Missed out correction from 6ac75c1

[tamird]

@alexcrichton it seems that sigaction.sa_flags and all the SA_* flags are signed here, but the linux headers disagree: https://github.com/torvalds/linux/blob/master/arch/mips/include/uapi/asm/signal.h#L105

Is this deviation intentional?

[alexcrichton]

@tamird it is indeed, we updated to a newer toolchain of MIPS which has change the type to int. As to why the kernel and libc disagree, I'm not sure.

[tamird]

Hm, seems odd. Another point of disagreement https://android.googlesource.com/platform/bionic/+/master/libc/kernel/uapi/asm-mips/asm/signal.h#96 nevermind, the android version is unsigned here.