Limit AST ID to FunctionDecl objects.

This should address the regression reported by @Machiry and discovered
by @hasantouma, and resolve #18.

Author: rchyena

tools/checked-c-convert/PersistentSourceLoc.cpp

@@ -19,15 +19,18 @@ using namespace llvm;
 PersistentSourceLoc
 PersistentSourceLoc::mkPSL(const Decl *D, ASTContext &C) {
   SourceLocation SL = D->getLocation();
+  int64_t funcID = -1;
 
-  if (const FunctionDecl *FD = dyn_cast<FunctionDecl>(D)) 
+  if (const FunctionDecl *FD = dyn_cast<FunctionDecl>(D)) {
     SL = C.getSourceManager().getSpellingLoc(FD->getLocation());
+    funcID = D->getID();  // Only incorporate AST IDs to distinguish functions.
+  }
   else if (const ParmVarDecl *PV = dyn_cast<ParmVarDecl>(D)) 
     SL = C.getSourceManager().getSpellingLoc(PV->getLocation());
   else if (const VarDecl *V = dyn_cast<VarDecl>(D))
     SL = C.getSourceManager().getExpansionLoc(V->getLocation());
 
-  return mkPSL(D->getSourceRange(), SL, D->getID(), C);
+  return mkPSL(D->getSourceRange(), SL, funcID, C);
 }