x86, boot: zero EFLAGS on 32 bits

The 64-bit code already clears EFLAGS as soon as it has a stack.  This
seems like a reasonable precaution, so do it on 32 bits as well.

[ Impact: extra paranoia ]
Signed-off-by: NH. Peter Anvin <hpa@zytor.com>

arch/x86/boot/compressed/head_32.S

@@ -91,6 +91,10 @@ ENTRY(startup_32)
 	/* Set up the stack */
 	leal	boot_stack_end(%ebx), %esp
 
+	/* Zero EFLAGS */
+	pushl	$0
+	popfl
+
 /*
  * Copy the compressed kernel to the end of our buffer
  * where decompression in place becomes safe.