Cleanup quick_exit tests and get them passing in C++03.

Wrap the original test in _LIBCPP_HAS_QUICK_EXIT so it only runs when we have
quick_exit and add two new tests that check that when _LIBCPP_HAS_QUICK_EXIT
is not defined then no definition of std::at_quick_exit or std::quick_exit are
available.


git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@222298 91177308-0d34-0410-b5e6-96231b3b80d8

test/language.support/support.start.term/quick_exit.pass.cpp

@@ -12,12 +12,13 @@
 // test quick_exit and at_quick_exit
 
 #include <cstdlib>
-#include <type_traits>
 
 void f() {}
 
 int main()
 {
+#ifdef _LIBCPP_HAS_QUICK_EXIT
     std::at_quick_exit(f);
-    quick_exit(0);
+    std::quick_exit(0);
+#endif
 }