pgsql: Some const qualifications added in passing

Some const qualifications added in passing

These are some cases in the vicinity of the patches to improve the
size_t/ssize_t use with POSIX file system APIs. For example, the
input buffers for write operations or the file names passed for error
reporting can be const.

Reviewed-by: Heikki Linnakangas <hlinnaka(at)iki(dot)fi>
Discussion: https://www.postgresql.org/message-id/flat/f9aab072-0078-49e4-ab93-3b08086a4406(at)eisentraut(dot)org

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/7f77b2a89bd4788b6bd686ba63138f51302d9839

Modified Files
--------------
src/backend/access/transam/timeline.c | 4 ++--
src/backend/access/transam/twophase.c | 4 ++--
src/bin/pg_basebackup/receivelog.c | 2 +-
src/bin/pg_combinebackup/reconstruct.c | 40 +++++++++++++++++-----------------
src/include/access/timeline.h | 4 ++--
5 files changed, 27 insertions(+), 27 deletions(-)