UAPI: Strip _UAPI prefix on header install no matter the whitespace

Commit 56c176c ("UAPI: strip the _UAPI prefix from header guards
during header installation") strips the _UAPI prefix from header guards,
but only if there's a single space between the cpp directive and the
label.

Make it more flexible and able to handle tabs and multiple white space
characters.

Signed-off-by: David Howells <dhowell@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

scripts/headers_install.pl

@@ -42,9 +42,9 @@
 		$line =~ s/(^|\s)(inline)\b/$1__$2__/g;
 		$line =~ s/(^|\s)(asm)\b(\s|[(]|$)/$1__$2__$3/g;
 		$line =~ s/(^|\s|[(])(volatile)\b(\s|[(]|$)/$1__$2__$3/g;
-		$line =~ s/#ifndef _UAPI/#ifndef /;
-		$line =~ s/#define _UAPI/#define /;
-		$line =~ s!#endif /[*] _UAPI!#endif /* !;
+		$line =~ s/#ifndef\s+_UAPI/#ifndef /;
+		$line =~ s/#define\s+_UAPI/#define /;
+		$line =~ s!#endif\s+/[*]\s*_UAPI!#endif /* !;
 		printf {$out} "%s", $line;
 	}
 	close $out;