fix libc-internal signal blocking on mips archs

due to historical reasons, the mips signal set has 128 bits rather
than 64 like on every other arch. this was special-cased correctly, at
least for 32-bit mips, at one time, but was inadvertently broken in
commit 7c440977db, and seems never to
have been right on mips64/n32.

as consequenct of this bug, applications making use of high realtime
signal numbers on mips may have been able to execute application code
in contexts where doing so was unsafe.

src/signal/block.c

@@ -3,9 +3,9 @@
 #include <signal.h>
 
 static const unsigned long all_mask[] = {
-#if ULONG_MAX == 0xffffffff && _NSIG == 129
+#if ULONG_MAX == 0xffffffff && _NSIG > 65
 	-1UL, -1UL, -1UL, -1UL
-#elif ULONG_MAX == 0xffffffff
+#elif ULONG_MAX == 0xffffffff || _NSIG > 65
 	-1UL, -1UL
 #else
 	-1UL