fltk: add devel build.

Closes #44806.

Library/Formula/fltk.rb

@@ -1,8 +1,26 @@
 class Fltk < Formula
   desc "Cross-platform C++ GUI toolkit"
   homepage "http://www.fltk.org/"
-  url "https://fossies.org/linux/misc/fltk-1.3.3-source.tar.gz"
-  sha256 "f8398d98d7221d40e77bc7b19e761adaf2f1ef8bb0c30eceb7beb4f2273d0d97"
+  revision 1
+
+  stable do
+    url "https://fossies.org/linux/misc/fltk-1.3.3-source.tar.gz"
+    sha256 "f8398d98d7221d40e77bc7b19e761adaf2f1ef8bb0c30eceb7beb4f2273d0d97"
+    depends_on MaximumMacOSRequirement => :yosemite
+
+    # Fixes issue with -lpng not found.
+    # Based on: https://trac.macports.org/browser/trunk/dports/aqua/fltk/files/patch-src-Makefile.diff
+    patch :DATA
+  end
+
+  devel do
+    url "http://fltk.org/pub/fltk/snapshots/fltk-1.3.x-r10866.tar.gz"
+    sha256 "4fd4911a1da99c2fa1e6cc0c985b3b8645a7e954802230338fb513ae880ff2cc"
+    version "1.3.3-r10866" # convince brew that this is older than stable
+
+    depends_on "autoconf" => :build
+    depends_on "autogen" => :build
+  end
 
   bottle do
     sha1 "33c75cce41deadbfe54bdcc22ae91d17d3ecc782" => :mavericks
@@ -14,20 +32,15 @@ class Fltk < Formula
   depends_on "libpng"
   depends_on "jpeg"
 
-  # Fltk 1.3.4 include support for El Capitan. Remove on update.
-  depends_on MaximumMacOSRequirement => :yosemite
-
   fails_with :clang do
     build 318
     cause "http://llvm.org/bugs/show_bug.cgi?id=10338"
   end
 
-  # Fixes issue with -lpng not found.
-  # Based on: https://trac.macports.org/browser/trunk/dports/aqua/fltk/files/patch-src-Makefile.diff
-  patch :DATA
-
   def install
     ENV.universal_binary if build.universal?
+
+    system "NOCONFIGURE=1 ./autogen.sh" if build.devel?
     system "./configure", "--prefix=#{prefix}",
                           "--enable-threads",
                           "--enable-shared"