webkitgtk24x: fix libwebp missing library path, add libobjc as dependency on OSX (#17198)

pkgs/development/libraries/webkitgtk/configure.patch

@@ -0,0 +1,20 @@
+--- webkitgtk-2.4.11-orig/configure	2016-04-10 17:00:06.000000000 +0800
++++ webkitgtk-2.4.11/configure	2016-07-21 23:04:10.000000000 +0800
+@@ -17738,7 +17738,7 @@
+   cat >>confdefs.h <<_ACEOF
+ #define HAVE_WEBP_DECODE_H 1
+ _ACEOF
+- WEBP_LIBS='-lwebp'
++ WEBP_LIBS=`$PKG_CONFIG --libs libwebp`
+ else
+   as_fn_error $? "WebP library (libwebp) not found" "$LINENO" 5
+ fi
+@@ -18388,7 +18388,7 @@
+ case "$host" in
+     *-*-darwin*)
+         UNICODE_CFLAGS="-I$srcdir/Source/JavaScriptCore/icu -I$srcdir/Source/WebCore/icu"
+-        UNICODE_LIBS="-licucore"
++        UNICODE_LIBS="/usr/lib/libicucore.dylib"
+         ;;
+     *-*-mingw*)
+