Clear up some object lifetime issues for ASTContext and Preprocessor.

Bug: 18343568
https://code.google.com/p/android/issues/detail?id=79142

llvm-rs-cc was accidentally freeing memory that was still in use. The
ASTContext and Preprocessor contain several strings and other pieces
of data that are used during the generation of our reflected code.

(cherry picked from commit c546630bbcc631bc963609c2288d4d9a18753e8d)

Change-Id: I900faa3beb6b1e21524708ca2a23468da1de6011
diff --git a/slang.cpp b/slang.cpp
index c3ab7e6..039b17a 100644
--- a/slang.cpp
+++ b/slang.cpp
@@ -452,8 +452,6 @@
 
   // The compilation ended, clear
   mBackend.reset();
-  mASTContext.reset();
-  mPP.reset();
   mOS.reset();
 
   return mDiagEngine->hasErrorOccurred() ? 1 : 0;