add back NSIG, removed from powerpc in last commit, but for all archs

unlike the previous definition, NSIG/_NSIG is supposed to be one more
than the highest signal number. adding this will allow simplifying
libc-internal code that makes signal-related syscalls, which can be
done as a later step. some apps might use it too; while this usage is
questionable, it's at least not insane.

arch/arm/bits/signal.h

@@ -71,3 +71,5 @@ struct sigcontext
 #define SIGPWR    30
 #define SIGSYS    31
 #define SIGUNUSED SIGSYS
+
+#define _NSIG 65

arch/i386/bits/signal.h

@@ -80,3 +80,5 @@ struct sigcontext {
 #define SIGPWR    30
 #define SIGSYS    31
 #define SIGUNUSED SIGSYS
+
+#define _NSIG 65

arch/microblaze/bits/signal.h

@@ -73,3 +73,5 @@ struct sigcontext
 #define SIGPWR    30
 #define SIGSYS    31
 #define SIGUNUSED SIGSYS
+
+#define _NSIG 65

arch/mips/bits/signal.h

@@ -82,3 +82,5 @@ struct sigcontext
 #define SIGXCPU   30
 #define SIGXFSZ   31
 #define SIGUNUSED SIGSYS
+
+#define _NSIG 129

arch/powerpc/bits/signal.h

@@ -114,3 +114,5 @@ typedef struct __ucontext {
 #define SIGPWR    30
 #define SIGSYS    31
 #define SIGUNUSED SIGSYS
+
+#define _NSIG 65

arch/x86_64/bits/signal.h

@@ -78,3 +78,5 @@ struct sigcontext {
 #define SIGPWR    30
 #define SIGSYS    31
 #define SIGUNUSED SIGSYS
+
+#define _NSIG 65