Move compiler warning suppression for tests from cpp files to CMake

tests/notnull_tests.cpp

@@ -23,19 +23,6 @@
 #pragma warning(disable : 4702) // unreachable code
 #endif
 
-#if __clang__ || __GNUC__
-//disable warnings from gtest
-#pragma GCC diagnostic push
-#pragma GCC diagnostic ignored "-Wundef"
-#endif // __clang__ || __GNUC__
-
-#if __clang__
-#pragma GCC diagnostic ignored "-Wglobal-constructors"
-#pragma GCC diagnostic ignored "-Wused-but-marked-unused"
-#pragma GCC diagnostic ignored "-Wcovered-switch-default"
-#pragma GCC diagnostic ignored "-Winconsistent-missing-destructor-override"
-#endif // __clang__
-
 #include <gtest/gtest.h>
 
 #include <gsl/pointers> // for not_null, operator<, operator<=, operator>
@@ -558,7 +545,3 @@ TEST(notnull_tests, TestMakeNotNull)
 
 static_assert(std::is_nothrow_move_constructible<not_null<void*>>::value,
               "not_null must be no-throw move constructible");
-
-#if __clang__ || __GNUC__
-#pragma GCC diagnostic pop
-#endif // __clang__ || __GNUC__