makepkg: Only check regular files in $srcdir check

The 'grep -R' in the $srcdir check would not only grep regular files,
but also devices, symlinks (that might potentially point outside of
$pkgdir), pipes and so on. Use find to ensure only regular files are
examined.

This should fix https://bugs.archlinux.org/task/19975

Signed-off-by: Allan McRae <allan@archlinux.org>

scripts/makepkg.sh.in

@@ -980,7 +980,7 @@ check_package() {
 	done
 
 	# check for references to the build directory
-	if grep -R "${srcdir}" "${pkgdir}" &>/dev/null; then
+	if find "${pkgdir}" -type f -exec grep -q "${srcdir}" {} +; then
 		warning "$(gettext "Package contains reference to %s")" "\$srcdir"
 	fi
 }