Elevate .text.syscall to .privileged

It turns out adding OpenBSD msyscall() origin verification broke the
--ftrace flag. The executable needs to issue raw syscalls while it's
rewriting itself. So they need to be in the same section, and that's
just plain simpler too.

libc/runtime/stackchkfail.c

@@ -28,7 +28,7 @@
 /**
  * Aborts program under enemy fire to avoid being taken alive.
  */
-textsyscall noasan void __stack_chk_fail(void) {
+privileged noasan void __stack_chk_fail(void) {
   size_t len;
   const char *msg;
   int64_t ax, cx, si;