Update GettingStarted.md

Clarified LLVM and Clang revisions needed.

docs/GettingStarted.md

@@ -25,7 +25,11 @@ Git repository urls found here: [http://llvm.org/docs/GettingStarted.html#git-mi
 Building in *Release* is recommended because else the Clang parser will be
 excruciatingly slow.
 
-Last updated to LLVM/Clang revision: `r202563`
+Due to some incompatible changes in recent LLVM versions, Windows builds need to use the following set of revisions that are known to work.
+
+LLVM `r202563` / Git mirror revision `c9bf74fdc543c2da90f334e0bf8e34b128c8a615`.
+
+Clang `r202562` / Git mirror revision `30577e6c4f5ba66b8dc832ed9955b1a7475f788a`.
 
 ## Compiling on Mac OS X (experimental)
 
@@ -548,4 +552,4 @@ Hopefully now you have a better idea of how the generator works and how to
 setup simple customizations to get the outputs better mapped to .NET. 
 
 This barely touched the surface of what can be done with CppSharp, so please
-check out the user and developer reference manuals for more information. 
+check out the user and developer reference manuals for more information.