pgsql: Add log file support to logging.c

Add log file support to logging.c

This adds the ability for users of logging.c to provide a file handle
for a log file, where log messages are also written in addition to
stderr.

Reviewed-by: Amit Kapila <amit.kapila16@gmail.com>
Discussion: /messages/by-id/CAEqnbaUthOQARV1dscGvB_EsqC-YfxiM6rWkVDHc+G+f4oSUHw@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/41237556f8c554f691968dbdce5fa6f4012e8036

Modified Files
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src/common/logging.c | 27 +++++++++++++++++++++++++++
src/include/common/logging.h | 2 ++
2 files changed, 29 insertions(+)