Prevent compilation of frontend-only files in src/common/ with backend
Any frontend-only file of src/common/ should include a protection to
prevent such code to be included in the backend compilation.
fe_memutils.c and restricted_token.c have been doing that, while
file_utils.c (since
bf5bb2e) and logging.c (since
fc9a62a) forgot it.
Reviewed-by: Daniel Gustafsson
Discussion: https://postgr.es/m/
20200625080757.GI130132@paquier.xyz