shadow: make this build with musl.

srcpkgs/shadow/template

@@ -38,6 +38,13 @@ if [ "$CROSS_BUILD" ]; then
 	}
 fi
 
+pre_configure() {
+	case "$XBPS_TARGET_MACHINE" in
+		# Completely disable unportable ruserok().
+		*-musl) sed '/RUSEROK/d' -i configure;;
+	esac
+}
+
 do_build() {
 	# Don't install groups(1), we use the one from coreutils.
 	sed -i 's/groups$(EXEEXT) //' src/Makefile