Fix clang-tidy warnings. (#4149)

* Upgrade gtest for clang-tidy.
* Use CMake to install GTest instead of mv.
* Don't enforce clang-tidy to return 0 due to errors in thrust.
* Add a small test for tidy itself.

* Reformat.

tests/ci_build/test_tidy.cc

@@ -0,0 +1,11 @@
+#include <iostream>
+#include <vector>
+
+struct Foo {
+  int bar_;
+};
+
+int main() {
+  std::vector<Foo> values;
+  values.push_back(Foo());
+}