pgsql: Fix erroneous -Werror=missing-braces on old GCC

Fix erroneous -Werror=missing-braces on old GCC

The buildfarm reports that this is an error on gcc (Debian 4.7.2-5)
4.7.2, 32-bit. The bug seems to be GCC bug 53119, which has obviously
been fixed for years.

Author: Tristan Partin <tristan@neon.tech>
Discussion: https://www.postgresql.org/message-id/flat/CT6HJ3U8068R.3A8SJMV02D9BC@gonk

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/5e0c761d0a13c7b4f7c5de618ac38560d74d74d0

Modified Files
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src/bin/pgbench/pgbench.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)