imagemagick: add fontconfig option.

Closes Homebrew#15417.

Library/Formula/imagemagick.rb

@@ -35,13 +35,15 @@ class Imagemagick < Formula
   option 'with-quantum-depth-16', 'Compile with a quantum depth of 16 bit'
   option 'with-quantum-depth-32', 'Compile with a quantum depth of 32 bit'
   option 'with-x', 'Compile with X11 support.'
+  option 'with-fontconfig', 'Compile with fontconfig support.'
   option 'without-freetype', 'Compile without freetype support.'
 
   depends_on 'pkg-config' => :build
 
   depends_on 'jpeg' => :recommended
   depends_on :libpng
   depends_on :x11 if build.include? 'with-x'
+  depends_on :fontconfig => :optional if build.include? 'with-fontconfig' or MacOS::X11.installed?
   depends_on :freetype => :recommended unless build.include? 'without-freetype'
 
   depends_on 'ghostscript' => :optional if ghostscript_srsly?
@@ -100,6 +102,7 @@ def install
     args << "--with-quantum-depth=#{quantum_depth}" if quantum_depth
     args << "--with-rsvg" if build.include? 'use-rsvg'
     args << "--without-x" unless build.include? 'with-x'
+    args << "--with-fontconfig=yes" if build.include? 'with-fontconfig'
     args << "--with-freetype=yes" if build.include? 'with-freetype'
 
     # versioned stuff in main tree is pointless for us