ocaml: add fix for GC crash in 4.02.2

Upstream fix in http://caml.inria.fr/mantis/view.php?id=6919.
Also add some hints on packaging as requested in Homebrew/homebrew#41432

Formula/objective-caml.rb

@@ -1,9 +1,23 @@
+# OCaml does not preserve binary compatibility across compiler releases,
+# so when updating it you should ensure that all dependent packages are
+# also updated by incrementing their revisions.
+#
+# Specific packages to pay attention to include:
+# - camlp4
+# - opam
+#
+# Applications that really shouldn't break on a compiler update are:
+# - mldonkey
+# - coq
+# - coccinelle
+# - unison
 class ObjectiveCaml < Formula
   desc "General purpose programming language in the ML family"
   homepage "https://ocaml.org/"
   url "http://caml.inria.fr/pub/distrib/ocaml-4.02/ocaml-4.02.2.tar.bz2"
   sha256 "b18265582b1c2fd5c1e67da3f744bf1ff474d194bb277c3a9ceb5eb16a1ea703"
   head "http://caml.inria.fr/svn/ocaml/trunk", :using => :svn
+  revision 1
 
   bottle do
     sha256 "b9cb85c9c8a838217699388af2ac50e6691dc7343889015c23f88c61dd4c227f" => :yosemite
@@ -15,6 +29,10 @@ class ObjectiveCaml < Formula
 
   depends_on :x11 => :optional
 
+  # Upstream fix for a GC crash issue introduced in 4.02.2
+  # See http://caml.inria.fr/mantis/view.php?id=6919
+  patch :DATA
+
   def install
     ENV.deparallelize # Builds are not parallel-safe, esp. with many cores
 
@@ -32,3 +50,17 @@ class ObjectiveCaml < Formula
     assert_match "#{HOMEBREW_PREFIX}", shell_output("ocamlc -where")
   end
 end
+__END__
+diff --git a/byterun/minor_gc.c b/byterun/minor_gc.c
+index 4aaec96..859a72a 100644
+--- a/byterun/minor_gc.c
++++ b/byterun/minor_gc.c
+@@ -259,6 +259,8 @@ void caml_empty_minor_heap (void)
+     ++ caml_stat_minor_collections;
+     caml_final_empty_young ();
+     if (caml_minor_gc_end_hook != NULL) (*caml_minor_gc_end_hook) ();
++  } else {
++    caml_final_empty_young ();
+   }
+ #ifdef DEBUG
+   {