[analyzer] Refactor checkers to use helper function for getting callee Decl and name.

We are getting name of the called function or it's declaration in a few checkers. Refactor them to use the helper function in the CheckerContext. 

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@145576 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/StaticAnalyzer/Checkers/PthreadLockChecker.cpp b/lib/StaticAnalyzer/Checkers/PthreadLockChecker.cpp
index c02b5b1..45988f0 100644
--- a/lib/StaticAnalyzer/Checkers/PthreadLockChecker.cpp
+++ b/lib/StaticAnalyzer/Checkers/PthreadLockChecker.cpp
@@ -57,18 +57,10 @@
 void PthreadLockChecker::checkPostStmt(const CallExpr *CE,
                                        CheckerContext &C) const {
   const ProgramState *state = C.getState();
-  const Expr *Callee = CE->getCallee();
-  const FunctionDecl *FD = state->getSVal(Callee).getAsFunctionDecl();
-
-  if (!FD)
+  StringRef FName = C.getCalleeName(CE);
+  if (FName.empty())
     return;
 
-  // Get the name of the callee.
-  IdentifierInfo *II = FD->getIdentifier();
-  if (!II)   // if no identifier, not a simple C function
-    return;
-  StringRef FName = II->getName();
-
   if (CE->getNumArgs() != 1)
     return;