fontconfig: add font dirs in Library to config

Fontconfig does not cache fonts in /Library/Fonts and ~/Library/Fonts.
The patch fixes this.

Closes Homebrew/homebrew#15745.

Signed-off-by: Mike McQuaid <mike@mikemcquaid.com>

Formula/fontconfig.rb

@@ -19,7 +19,7 @@ class Fontconfig < Formula
 
   def install
     ENV.universal_binary if build.universal?
-    system "./configure", "--disable-dependency-tracking", "--prefix=#{prefix}"
+    system "./configure", "--disable-dependency-tracking", "--with-add-fonts=/Library/Fonts,~/Library/Fonts", "--prefix=#{prefix}"
     system "make install"
   end
 end