x86: switch sigframe sigset handling to explict __get_user()/__put_user()

... and consolidate the definition of sigframe_ia32->extramask - it's
always a 1-element array of 32bit unsigned.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

arch/x86/include/asm/sigframe.h

@@ -33,11 +33,7 @@ struct sigframe_ia32 {
 	 * legacy application accessing/modifying it.
 	 */
 	struct _fpstate_32 fpstate_unused;
-#ifdef CONFIG_IA32_EMULATION
-	unsigned int extramask[_COMPAT_NSIG_WORDS-1];
-#else /* !CONFIG_IA32_EMULATION */
-	unsigned long extramask[_NSIG_WORDS-1];
-#endif /* CONFIG_IA32_EMULATION */
+	unsigned int extramask[1];
 	char retcode[8];
 	/* fp state follows here */
 };