Add libffi build scripts and patch for borked mozilla-build script

win32/deps/mozilla-build.patch

@@ -0,0 +1,20 @@
+--- start-msvc11-x64.bat.orig	2012-07-18 19:44:24 +0200
++++ start-msvc11-x64.bat	2012-09-30 17:48:59 +0200
+@@ -30,7 +30,7 @@
+     )
+ 
+     rem Prepend MSVC paths
+-    call "%VC11EXPRESSDIR%\bin\amd64\vcvars64.bat" 2>nul
++    call "%VC11EXPRESSDIR%\bin\x86_amd64\vcvarsx86_amd64.bat" 2>nul
+     if "%DevEnvDir%"=="" (
+       rem Might be using a compiler that shipped with an SDK, so manually set paths
+       SET "PATH=%VC11EXPRESSDIR%\Bin\amd64;%VC11EXPRESSDIR%\Bin;%PATH%"
+@@ -58,7 +58,7 @@
+     rem Prepend MSVC paths
+     rem The Win7 SDK (or newer) should automatically integrate itself into vcvars32.bat
+     ECHO Using VC 2012 built-in SDK
+-    call "%VC11DIR%\bin\amd64\vcvars64.bat"
++    call "%VC11DIR%\bin\x86_amd64\vcvarsx86_amd64.bat"
+ )
+ 
+ if "%VC11DIR%"=="" (