[PCH] Make the const_cast explicit to silence a compiler warning.

Patch by David Greene.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@172262 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Serialization/ASTReader.cpp b/lib/Serialization/ASTReader.cpp
index f32d53f..a4436d1 100644
--- a/lib/Serialization/ASTReader.cpp
+++ b/lib/Serialization/ASTReader.cpp
@@ -655,7 +655,8 @@
                                         unsigned DataLen) {
   using namespace clang::io;
   unsigned NumDecls = ReadUnalignedLE16(d);
-  LE32DeclID *Start = (LE32DeclID *)d;
+  LE32DeclID *Start = reinterpret_cast<LE32DeclID *>(
+                        const_cast<unsigned char *>(d));
   return std::make_pair(Start, Start + NumDecls);
 }