TEMPLATE_TEST_CASE triggers -Wunused-template with clang 8

[aza-ableton]

The -Wunused-template warning is triggered by the expansion of the TEMPLATE_TEST_CASE macro. This prevents enabling that warning in client code.

Expected behavior
TEMPLATE_TEST_CASE tests compile without warnings when -Wunused-template is enabled in client code.

Reproduction steps
Compile the following with clang 8 or later using -Weverything -Wno-c++98-compat or just -Wunused-template:

// ignore all warnings in Catch internal code
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Weverything"
#include "catch.hpp"
#pragma clang diagnostic pop

TEMPLATE_TEST_CASE("T", "[]", int)
{
}

Platform information:
I have seen this on OS X Mojave using XCode 10.2.1, but it seems to occur on other platforms as well and with later clang versions. See https://godbolt.org/z/wO8_HD