pgsql: Fix headerscheck and cpluspluscheck's exit codes.

Fix headerscheck and cpluspluscheck's exit codes.

For the benefit of CI, which started running these header check scripts
in its CompilerWarnings task in commit 81b9f23c9c8, they should report
failure if any individual header failed to compile.

Reviewed-by: Andrew Dunstan <andrew@dunslane.net>
Reviewed-by: Andres Freund <andres@anarazel.de>
Discussion: https://postgr.es/m/CA%2BhUKGKtDwPo9wzKgbStDwfOhEpywMc6PQofio8fAHR7yUjgxw%40mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/3eae0cbf7e70db885c4ec37e0863022d3ad589d4

Modified Files
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src/tools/pginclude/cpluspluscheck | 10 ++++++++--
src/tools/pginclude/headerscheck   | 10 ++++++++--
2 files changed, 16 insertions(+), 4 deletions(-)