Make it clear that GCMole depends on Clang 2.9 currently.

tools/gcmole/README

 DESCRIPTION -------------------------------------------------------------------
 
 gcmole is a simple static analysis tool used to find possible evaluation order 
 dependent GC-unsafe places in the V8 codebase.
 
 For example the following code is GC-unsafe:
 
 Handle<Object> Foo();  // Assume Foo can trigger a GC.
 void Bar(Object*, Object*);
 
 Handle<Object> baz;
 baz->Qux(*Foo());  // (a)  
 Bar(*Foo(), *baz);  // (b)
 
 Both in cases (a) and (b) compiler is free to evaluate call arguments (that 
 includes receiver) in any order. That means it can dereference baz before 
 calling to Foo and save a raw pointer to a heap object in the register or 
 on the stack.  
 
 PREREQUISITES -----------------------------------------------------------------
 
 1) Install Lua 5.1
 
-2) Get LLVM and Clang sources and build them. 
+2) Get LLVM 2.9 and Clang 2.9 sources and build them.
 
 Follow the instructions on http://clang.llvm.org/get_started.html.
 
 Make sure to pass --enable-optimized to configure to get Release build 
 instead of a Debug one.
 
 3) Build gcmole Clang plugin (libgcmole.so)
 
 In the tools/gcmole execute the following command:
 
@@ skipping 18 matching lines @@
 approximation to find all functions that might potentially cause GC, list
 of this functions will be written into gcsuspects file.
 
 - on the second stage driver will parse all files again and will locate all 
 callsites that might be GC-unsafe based on the list of functions causing GC. 
 Such places are marked with a "Possible problem with evaluation order." 
 warning. Messages "Failed to resolve v8::internal::Object" are benign and 
 can be ignored.
 
 If any errors were found driver exits with non-zero status.