Andres Freund <andres(at)anarazel(dot)de> writes:
> ATM the defines in pg_config_manual.h are largely unconditional - which
> means the file has to be edited instead of being able to override things
> via CFLAGS/COPT. Is there any good reason for doing so?
YES. If you do things like that, the installed version of
pg_config_manual.h will not reflect the way the backend was built,
which is likely to break pgxs-type builds of addon modules later.
Just edit the file.
regards, tom lane