[pgpool-committers: 5598] pgpool: Suppress useless truncation warnings from gcc 8+.

[Tatsuo Ishii]

Suppress useless truncation warnings from gcc 8+.

For this purpose update c-compiler.m4 (borrowed from PostgreSQL's
config/c-compiler.m4) and add PGAC_PROG_CC_VAR_OPT(NOT_THE_CFLAGS,
[-Wformat-truncation]) to configure.ac to generate -Wformat-truncation
compiler option.

Branch
------
V3_6_STABLE

Details
-------
https://git.postgresql.org/gitweb?p=pgpool2.git;a=commitdiff;h=700d9a309606a25ca648267df43d0812f60bf40e

Modified Files
--------------
c-compiler.m4 | 587 +++++++++++++++++++++++++++++++++++++++++++++++++++++++---
configure.ac  |   7 +
2 files changed, 569 insertions(+), 25 deletions(-)