Hide std::exception_ptr and friends if exceptions disabled

Some compilers, e.g. the Green Hills C++ compiler, react badly to the
appearance of std::exception_ptr, std::current_exception,
std::rethrow_exception and std::uncaught_exception(s). To allow usage of
Catch2 with these compilers when exceptions are disabled, hide the usage
of std::exception_ptr etc. when compiling with
CATCH_CONFIG_DISABLE_EXCEPTIONS.

include/internal/catch_registry_hub.cpp

@@ -59,7 +59,11 @@ namespace Catch {
                 m_tagAliasRegistry.add( alias, tag, lineInfo );
             }
             void registerStartupException() noexcept override {
+#if !defined(CATCH_CONFIG_DISABLE_EXCEPTIONS)
                 m_exceptionRegistry.add(std::current_exception());
+#else
+                CATCH_INTERNAL_ERROR("Attempted to register active exception under CATCH_CONFIG_DISABLE_EXCEPTIONS!");
+#endif
             }
             IMutableEnumValuesRegistry& getMutableEnumValuesRegistry() override {
                 return m_enumValuesRegistry;