pgsql: pg_upgrade: remove C99 compiler req. from commit 3c0471b5fd

pg_upgrade: remove C99 compiler req. from commit 3c0471b5fd

This commit required support for inline variable definition, which is
not a requirement.

RELEASE NOTE AUTHOR: the author of commit 3c0471b5fd
(pg_upgrade/tablespaces) was Justin Pryzby, not me.

Reported-by: Andres Freund

Discussion: /messages/by-id/20201016001959.h24fkywfubkv2pc5@alap3.anarazel.de

Backpatch-through: 9.5

Branch
------
REL9_5_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/b05672c725d62760ce7cba1150975b17aba5e29b

Modified Files
--------------
src/bin/pg_upgrade/check.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)