FindThreads cmake "error" in xtensor/test

[billpriest]

In building the tests for xtensor I saw the following:
xtensor/test > cmake .
CMake Error at /usr/share/cmake-3.20/Modules/FindThreads.cmake:66 (message):
FindThreads only works if either C or CXX language is enabled
Call Stack (most recent call first):
CMakeLists.txt:13 (find_package)

The following "hack" fixed the issue
diff --git a/test/CMakeLists.txt b/test/CMakeLists.txt
index 6e5cc7b9..2b64ed5a 100644
--- a/test/CMakeLists.txt
+++ b/test/CMakeLists.txt
@@ -9,9 +9,6 @@

cmake_minimum_required(VERSION 3.1)

-find_package(doctest REQUIRED)
-find_package(Threads)

if (CMAKE_CURRENT_SOURCE_DIR STREQUAL CMAKE_SOURCE_DIR)
project(xtensor-test)

@@ -28,6 +25,9 @@ else()
message(STATUS "Tests build type is ${CMAKE_BUILD_TYPE}")
endif()

+find_package(doctest REQUIRED)
+find_package(Threads)
+
include(CheckCXXCompilerFlag)

string(TOUPPER "${CMAKE_BUILD_TYPE}" U_CMAKE_BUILD_TYPE)

I'm also seeing issues when building wrt TEST_CASE_TEMPLATE (although I expect this is just having the wrong version of the test library; it would be nice if the CMakeLists.txt error'ed out unless the correct version is found).