Add proper CMake setup

This adds a CMake library and a test for it. We now explicitly pull in a
specific version of GTest for testing.

cc/src/CMakeLists.txt

@@ -0,0 +1,33 @@
+cmake_minimum_required(VERSION 3.14)
+project(gnumake-tokenpool LANGUAGES CXX)
+
+add_library(
+    gnumake-tokenpool
+    tokenpool-gnu-make-posix.cc
+    # tokenpool-gnu-make-win32.cc # TODO: Add this file iff building on win32.
+    tokenpool-gnu-make.cc)
+target_include_directories(gnumake-tokenpool PUBLIC ${CMAKE_CURRENT_SOURCE_DIR})
+
+option(GNUMAKE_TOKENPOOL_BUILD_TESTS "build gnumake-tokenpool tests" ON)
+
+if (GNUMAKE_TOKENPOOL_BUILD_TESTS)
+    # GoogleTest requires at least C++14
+    set(CMAKE_CXX_STANDARD 14)
+    set(CMAKE_CXX_STANDARD_REQUIRED ON)
+
+    include(FetchContent)
+    FetchContent_Declare(
+        googletest
+        URL https://github.com/google/googletest/releases/download/v1.15.2/googletest-1.15.2.tar.gz)
+    # For Windows: Prevent overriding the parent project's compiler/linker settings
+    set(gtest_force_shared_crt ON CACHE BOOL "" FORCE)
+    FetchContent_MakeAvailable(googletest)
+
+    add_executable(gnumake-tokenpool-test tokenpool_test.cc)
+    target_link_libraries(gnumake-tokenpool-test gnumake-tokenpool gtest_main)
+
+    enable_testing()
+
+    include(GoogleTest)
+    gtest_discover_tests(gnumake-tokenpool-test)
+endif ()

cc/src/tokenpool_test.cc

@@ -14,7 +14,7 @@
 
 #include "tokenpool.h"
 
-#include "test.h"
+#include "gtest/gtest.h"
 
 #ifdef _WIN32
 #include <windows.h>