jmp_buf overhaul fixing several issues

on arm, the location of the saved-signal-mask flag and mask were off
by one between sigsetjmp and siglongjmp, causing incorrect behavior
restoring the signal mask. this is because the siglongjmp code assumed
an extra slot was in the non-sig jmp_buf for the flag, but arm did not
have this. now, the extra slot is removed for all archs since it was
useless.

also, arm eabi requires jmp_buf to have 8-byte alignment. we achieve
that using long long as the type rather than with non-portable gcc
attribute tags.

arch/arm/bits/setjmp.h

-typedef unsigned long jmp_buf [64];
+typedef unsigned long long jmp_buf[32];

arch/i386/bits/setjmp.h

-typedef unsigned long jmp_buf [7];
+typedef unsigned long jmp_buf[6];

arch/x86_64/bits/setjmp.h

-typedef unsigned long jmp_buf [9];
+typedef unsigned long jmp_buf[8];

include/setjmp.h

@@ -11,7 +11,11 @@ extern "C" {
 #if defined(_POSIX_SOURCE) || defined(_POSIX_C_SOURCE) \
  || defined(_XOPEN_SOURCE) || defined(_GNU_SOURCE) \
  || defined(_BSD_SOURCE)
-typedef unsigned long sigjmp_buf[(128+sizeof(jmp_buf))/sizeof(long)];
+typedef struct {
+	jmp_buf __jb;
+	unsigned long __fl;
+	unsigned long __ss[128];
+} sigjmp_buf[1];
 int sigsetjmp (sigjmp_buf, int);
 void siglongjmp (sigjmp_buf, int);
 #endif

src/signal/siglongjmp.c

 #include <setjmp.h>
 #include <signal.h>
 #include <stdlib.h>
+#include "syscall.h"
 
 void siglongjmp(sigjmp_buf buf, int ret)
 {
-	unsigned long *flag = buf + sizeof(jmp_buf)/sizeof(long) - 1;
-	sigset_t *mask = (void *)(flag + 1);
-	if (*flag)
-		sigprocmask (SIG_SETMASK, mask, NULL);
-	longjmp((void *)buf, ret);
+	if (buf->__fl)
+		__syscall(SYS_rt_sigprocmask, SIG_SETMASK, buf->__ss, 0, 8);
+	longjmp(buf->__jb, ret);
 }

src/signal/sigsetjmp.c

@@ -9,9 +9,7 @@
 
 int sigsetjmp(sigjmp_buf buf, int save)
 {
-	unsigned long *flag = buf + sizeof(jmp_buf)/sizeof(long);
-	sigset_t *mask = (void *)(flag + 1);
-	if ((*flag = save))
-		sigprocmask (SIG_SETMASK, NULL, mask);
-	return setjmp((void *)buf);
+	if ((buf->__fl = save))
+		pthread_sigmask(SIG_SETMASK, 0, (sigset_t *)buf->__ss);
+	return setjmp(buf->__jb);
 }