pgsql: Use macro to define the number of enum values

Use macro to define the number of enum values

Refactoring in the interest of code consistency, a follow-up to 2e068db56e31.

The argument against inserting a special enum value at the end of the enum
definition is that a switch statement might generate a compiler warning unless
it has a default clause.

Aleksander Alekseev, reviewed by Michael Paquier, Dean Rasheed, Peter Eisentraut

Discussion: https://postgr.es/m/CAJ7c6TMsiaV5urU_Pq6zJ2tXPDwk69-NKVh4AMN5XrRiM7N%2BGA%40mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/10b721821d6d6e27e594549cf105476dc28514c8

Modified Files
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contrib/pg_stat_statements/pg_stat_statements.c | 4 ++--
src/backend/postmaster/autovacuum.c             | 3 ++-
src/bin/pg_dump/pg_backup.h                     | 3 ++-
src/include/storage/pmsignal.h                  | 4 ++--
src/include/storage/procsignal.h                | 4 ++--
5 files changed, 10 insertions(+), 8 deletions(-)