This commit moves the timestamp computation of the control file within
the routine of src/common/ in charge of updating the backend's control
file, which is shared by multiple frontend tools (pg_rewind,
pg_checksums and pg_resetwal) and the backend itself.
This change has as direct effect to update the control file's timestamp
when writing the control file in pg_rewind and pg_checksums, something
that is helpful to keep track of control file updates for those
operations, something also tracked by the backend at startup within its
logs. This part is arguably a bug, as ControlFileData->time should be
updated each time a new version of the control file is written, but this
is a behavior change so no backpatch is done.
Author: Amul Sul
Reviewed-by: Nathan Bossart, Michael Paquier, Bharath Rupireddy
Discussion: https://postgr.es/m/CAAJ_b97nd_ghRpyFV9Djf9RLXkoTbOUqnocq11WGq9TisX09Fw@mail.gmail.com