Replace SVal llvm::cast support to be well-defined.

See r175462 for another example/more details.

llvm-svn: 175594
diff --git a/clang/lib/StaticAnalyzer/Checkers/PthreadLockChecker.cpp b/clang/lib/StaticAnalyzer/Checkers/PthreadLockChecker.cpp
index 8407ea4..ffb8cf2 100644
--- a/clang/lib/StaticAnalyzer/Checkers/PthreadLockChecker.cpp
+++ b/clang/lib/StaticAnalyzer/Checkers/PthreadLockChecker.cpp
@@ -98,7 +98,7 @@
   if (X.isUnknownOrUndef())
     return;
   
-  DefinedSVal retVal = cast<DefinedSVal>(X);
+  DefinedSVal retVal = X.castAs<DefinedSVal>();
 
   if (state->contains<LockSet>(lockR)) {
     if (!BT_doublelock)