Fix Windows filename format, etc. (#3873) (#4421)

* Ignore CLion project files and CMake outputs
* Supporting stripping file path that contains backslash
* Set /bigobj flag and increase stack size for windows platform
* Fix MSVC warnings

src/V3MergeCond.cpp

@@ -620,6 +620,7 @@ private:
         // LCOV_EXCL_START
         if (debug()) rhsp->dumpTree("Don't know how to fold expression: ");
         rhsp->v3fatalSrc("Should not try to fold this during conditional merging");
+        return nullptr;
         // LCOV_EXCL_STOP
     }