The tcc.tcz package in the 12.x x86 repo depends on the api headers for the Tiny Core v11 kernel ("linux-5.4_api_headers.tcz") instead of the headers for the v12 kernel ("linux-v5.10_api_headers.tcz").
Since the v11 kernel api headers tcz doesn't exist in the v12 repo, you can't install tcc without manually downloading it and its dependencies.