um: Don't mark stack executable

On one of my machines UML failed to start after enabling
SELinux.
UML failed to start because SELinux's execmod rule denies
executable pages on a modified file mapping.

Historically UML marks it's stack rwx.
AFAICT, these days this is no longer needed, so let's remove
PROT_EXEC.

Signed-off-by: Richard Weinberger <richard@nod.at>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

Author: richardweinberger

arch/um/os-Linux/util.c

@@ -20,8 +20,7 @@
 
 void stack_protections(unsigned long address)
 {
-	if (mprotect((void *) address, UM_THREAD_SIZE,
-		    PROT_READ | PROT_WRITE | PROT_EXEC) < 0)
+	if (mprotect((void *) address, UM_THREAD_SIZE, PROT_READ | PROT_WRITE) < 0)
 		panic("protecting stack failed, errno = %d", errno);
 }