Disable CMake unity builds

The don't work in scitokens-cpp, but they wouldn't speed up builds
much anyway, as there aren't a huge number of .cpp files per library.
So, don't bother to fix the multiple inclusions problems that unity
builds create, just disable the feature here.

Turning this off does allow scitokens-cpp to be built in a larger
project that does turn on unity builds globally.

CMakeLists.txt

@@ -13,6 +13,8 @@ set( CMAKE_MODULE_PATH "${PROJECT_SOURCE_DIR}/cmake;${CMAKE_MODULE_PATH}" )
 
 set( CMAKE_BUILD_TYPE RelWithDebInfo) # -g -O2
 
+set( CMAKE_UNITY_BUILD False)
+
 include(GNUInstallDirs)
 
 find_package( jwt-cpp REQUIRED )