gtkmm: add as-needed for linking

gtkmm/Pkgfile

@@ -6,7 +6,7 @@
 
 name=gtkmm
 version=2.24.4
-release=1
+release=2
 source=(http://ftp.gnome.org/pub/GNOME/sources/$name/${version%.*}/$name-$version.tar.xz)
 
 build() {
@@ -19,6 +19,8 @@ build() {
 		--disable-dependency-tracking \
 		--disable-documentation
 
+	sed -i -e 's/ -shared / -Wl,-O1,--as-needed\0/g' libtool
+
 	make
 	make DESTDIR=$PKG install
 }