Confused about C/C++ runtimes

Okay well it turns out I don’t need any of these libraries. I can just provide the C sources

add_executable(test 
	${CMAKE_CURRENT_SOURCE_DIR}/app.c
	${CMAKE_CURRENT_SOURCE_DIR}/platform.c
	${CMAKE_CURRENT_SOURCE_DIR}/out/codegen/host/src/default_lib0.c
	${CMAKE_CURRENT_SOURCE_DIR}/out/codegen/host/src/default_lib1.c
	${CMAKE_CURRENT_SOURCE_DIR}/out/runtime/src/runtime/crt/memory/page_allocator.c

)

and it builds and appears to run an inference.

Could someone please help me understand what the runtime is providing? Is it just for the host mode?