clang-tidy: fix warnings from version 7

Fix some warnings that are new since clang-tidy version 4, and update
`.clang-tidy` to suppress the rest.

Source/cmForEachCommand.cxx

@@ -38,7 +38,7 @@ bool cmForEachFunctionBlocker::IsFunctionBlocked(const cmListFileFunction& lff,
       // Remove the function blocker for this scope or bail.
       std::unique_ptr<cmFunctionBlocker> fb(
         mf.RemoveFunctionBlocker(this, lff));
-      if (!fb.get()) {
+      if (!fb) {
         return false;
       }