spdlog_setup tries to find spdlog but doesn't exist

[jjcasmar]

I have a cmake project which fetches spdlog from git using FetchContent. This effectively defines a spdlog::spdlog target since it includes spdlog CMakeLists into my project.

Then I also fetch spdlog_setup. This step fails because spdlog_setup assumes we are going to use spdlog from deps/spdlog or from system (via find_package(spdlog REQUIRED). Since there is no package in system, it fails.

If spdlog::spdlog target is already defined, it shouldn't call find_package(spdlog REQUIRED)