Fix/suppress bionic google-explicit-constructor warnings

* Add explicit to conversion constructors/operators

Bug: 28341362
Test: make with WITH_TIDY=1 DEFAULT_GLOBAL_TIDY_CHECKS=-*,google-explicit-constructor
Change-Id: Id1ad0327c1b8c6f094bcbb3ae599bc1f716b3f2f
diff --git a/tests/libs/thread_local_dtor2.cpp b/tests/libs/thread_local_dtor2.cpp
index 9b2b164..177c91b 100644
--- a/tests/libs/thread_local_dtor2.cpp
+++ b/tests/libs/thread_local_dtor2.cpp
@@ -30,7 +30,7 @@
 
 class TestClass {
  public:
-  TestClass(bool* flag) : flag_(flag) {}
+  explicit TestClass(bool* flag) : flag_(flag) {}
   ~TestClass() {
     *flag_ = true;
   }