abstract missing SYS_pause syscall with macros

newer archs lack the syscall. the pause() function accounted for this
with its own #ifdef, but that didn't allow use of the syscall directly
elsewhere, so move the logic to macros in src/internal/syscall.h where
it can be shared.

src/internal/syscall.h

@@ -391,6 +391,17 @@ static inline long __alt_socketcall(int sys, int sock, int cp, syscall_arg_t a,
 #define __sys_open_cp(...) __SYSCALL_DISP(__sys_open_cp,,__VA_ARGS__)
 #define sys_open_cp(...) __syscall_ret(__sys_open_cp(__VA_ARGS__))
 
+#ifdef SYS_pause
+#define __sys_pause() __syscall(SYS_pause)
+#define __sys_pause_cp() __syscall_cp(SYS_pause)
+#else
+#define __sys_pause() __syscall(SYS_ppoll, 0, 0, 0, 0)
+#define __sys_pause_cp() __syscall_cp(SYS_ppoll, 0, 0, 0, 0)
+#endif
+
+#define sys_pause() __syscall_ret(__sys_pause())
+#define sys_pause_cp() __syscall_ret(__sys_pause_cp())
+
 #ifdef SYS_wait4
 #define __sys_wait4(a,b,c,d) __syscall(SYS_wait4,a,b,c,d)
 #define __sys_wait4_cp(a,b,c,d) __syscall_cp(SYS_wait4,a,b,c,d)

src/unistd/pause.c

@@ -3,9 +3,5 @@
 
 int pause(void)
 {
-#ifdef SYS_pause
-	return syscall_cp(SYS_pause);
-#else
-	return syscall_cp(SYS_ppoll, 0, 0, 0, 0);
-#endif
+	return sys_pause_cp();
 }