Prefer C++-style casts.

This is based on Item 2 of "More Effective C++". In general, the C++ cast operators are more expressive and easy to find,
e.g. by grep. Using const_cast also shuts up some compiler warnings.

ir/irtypefunction.cpp

@@ -21,7 +21,7 @@ llvm::Type * IrTypeFunction::buildType()
 llvm::Type* IrTypeFunction::func2llvm(Type* dt)
 {
     llvm::Type* T;
-    TypeFunction* tf = (TypeFunction*)dt;
+    TypeFunction* tf = static_cast<TypeFunction*>(dt);
     if (tf->funcdecl)
         T = DtoFunctionType(tf->funcdecl);
     else