mono: Fix compile/runtime error on El Cap Beta 3

This fixes the error "could not discover the mach TLS offset" which
prohibits both running and compiling mono on OS X 10.11 (15A216g).

The patch was backported from current mono/mono master. Because the
problem also affects binaries compiled before upgrading to El Capitan
the patch is *not* scoped to `MacOS.version >= :el_capitan`.

Library/Formula/mono.rb

@@ -3,6 +3,7 @@ class Mono < Formula
   homepage "http://www.mono-project.com/"
   url "http://download.mono-project.com/sources/mono/mono-4.0.2.5.tar.bz2"
   sha256 "b074584eea5bbaaf29362486a69d70abe53d0d2feb334f231fa9c841cf6fd651"
+  revision 1
 
   # xbuild requires the .exe files inside the runtime directories to
   # be executable
@@ -14,6 +15,10 @@ class Mono < Formula
     sha256 "80bddaefcd9c136bc763797cff98f3aa07ec758e348037fd24f07d2b1b795fbb" => :mountain_lion
   end
 
+  # Fix compile and runtime error on OS X 10.11 Beta 3
+  # See: https://github.com/mono/mono/pull/1919
+  patch :DATA
+
   resource "monolite" do
     url "http://storage.bos.xamarin.com/mono-dist-4.0.0-release/c1/c1b37f29b1a439acf7ef42a384550ab1dca5295a/monolite-117-latest.tar.gz"
     sha256 "a3bd1c826186e4896193ad1f909bf8756f66f62d1e249fe301b10bc80ebe0795"
@@ -80,3 +85,37 @@ def caveats; <<-EOS.undent
     EOS
   end
 end
+
+__END__
+From c8a3c4fd36a69d039d0adb7da02de61e5e8df5f7 Mon Sep 17 00:00:00 2001
+From: "Craig S. Bosma" <craig.bosma@gmail.com>
+Date: Wed, 8 Jul 2015 19:01:55 -0500
+Subject: [PATCH] Add TLS offset for pre-release OS X 10.11 on amd64
+
+---
+ mono/utils/mach-support-amd64.c | 5 +++++
+ 1 file changed, 5 insertions(+)
+
+diff --git a/mono/utils/mach-support-amd64.c b/mono/utils/mach-support-amd64.c
+index 1904088..825f2a2 100644
+--- a/mono/utils/mach-support-amd64.c
++++ b/mono/utils/mach-support-amd64.c
+@@ -23,6 +23,7 @@
+ /* All OSX versions up to 10.8 */
+ #define TLS_VECTOR_OFFSET_CATS 0x60
+ #define TLS_VECTOR_OFFSET_10_9 0xe0
++#define TLS_VECTOR_OFFSET_10_11 0x100
+
+ static int tls_vector_offset;
+
+@@ -130,6 +131,10 @@ mono_mach_init (pthread_key_t key)
+ 	if (mono_mach_arch_get_tls_value_from_thread (pthread_self (), key) == canary)
+ 		goto ok;
+
++	tls_vector_offset = TLS_VECTOR_OFFSET_10_11;
++	if (mono_mach_arch_get_tls_value_from_thread (pthread_self (), key) == canary)
++		goto ok;
++
+ 	g_error ("could not discover the mach TLS offset");
+ ok:
+ 	pthread_setspecific (key, old_value);