Fix archetypes.hpp under libcpp-no-extensions and std level < 14

[rogfer01]

Summary

Under -fno-exceptions TEST_THROW becomes abort / __builtin_abort which returns void. This causes a type mismatch in the conditional operator when testing the library in C++98,03,11 modes.

This patch uses a comma operator to workaround this problem.

[EricWF]

Thanks!

libcxx/trunk/test/support/archetypes.hpp

TEST_CONSTEXPR_CXX14 ValueBase& operator=(int xvalue) noexcept {
         value = xvalue;
         return *this;
     }
     //~ValueBase() { assert(value != -999); value = -999; }
     int value;
 protected:
     constexpr static int check_value(int const& val) {
 #if TEST_STD_VER < 14
-      return val == -1 || val == 999 ? TEST_THROW(42) : val;
+      return val == -1 || val == 999 ? (TEST_THROW(42), 0) : val;
 #else
       assert(val != -1); assert(val != 999);
       return val;
 #endif
     }
     constexpr static int check_value(int& val, int val_cp = 0) {
 #if TEST_STD_VER < 14
-      return val_cp = val, val = -1, (val_cp == -1 || val_cp == 999 ? TEST_THROW(42) : val_cp);
+      return val_cp = val, val = -1, (val_cp == -1 || val_cp == 999 ? (TEST_THROW(42), 0) : val_cp);
 #else
       assert(val != -1); assert(val != 999);
       val_cp = val;
       val = -1;
       return val_cp;
 #endif
     }
     constexpr ValueBase() noexcept : value(0) {}