[libc++] Guard terminate_successful with TEST_HAS_NO_EXCEPTIONS

[ldionne]

Summary

This one is a bit twisted. Some platforms don't have support for
exiting in a clean manner, so they don't provide std::exit(). As
a result, defining terminate_successful() on those platforms won't
work, and the PSTL tests that rely on terminate_successful() also
won't work.

However, we don't have a notion of "no clean termination" in libc++,
so we can't properly guard this. Since embedded platforms that don't
support clean termination usually also don't enable exceptions, we
don't need to be able to run those terminate_successful PSTL tests,
and guarding the definition of terminate_successful with
TEST_HAS_NO_EXCEPTIONS works pretty well.

This is kind of a hack for the lack of having a concept of "no clean
termination" in the library and in the test suite.

[philnik]

I'm not a huge fan, but I also don't really see a nice way of solving this.

libcxx/test/support/test_execution_policies.h

struct Bool {
   Bool() = default;
   Bool(bool b) : b_(b) {}
 
   operator bool&() {
     return b_;
   }
 };
 
+#ifndef TEST_HAS_NO_EXCEPTIONS
 [[noreturn]] inline void terminate_successful() { std::exit(0); }
+#endif
 
 #endif // TEST_SUPPORT_TEST_EXECUTION_POLICIES