pgsql: Refactor get_collation_current_version().

Refactor get_collation_current_version().

The code paths for three different OSes finished up with three different
ways of excluding C[.xxx] and POSIX from consideration.  Merge them.

Reviewed-by: Michael Paquier <[hidden email]>
Discussion: https://postgr.es/m/20210117215940.GE8560%40telsasoft.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/beb4480c853a60ec43bd3f1a71252890dd234f10

Modified Files
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src/backend/utils/adt/pg_locale.c | 34 ++++------------------------------
1 file changed, 4 insertions(+), 30 deletions(-)