pgsql: Fix ac218aa4f6 to work on versions before 9.5.

Fix ac218aa4f6 to work on versions before 9.5.

Unfortunately ac218aa4f6 missed the fact that a reference to
'pg_catalog.regnamespace'::regclass wouldn't work before that type is
known. Fix that, by replacing the regtype usage with a join to
pg_type.

Reported-By: Tom Lane
Author: Andres Freund
Discussion: https://postgr.es/m/8863.1543297423@sss.pgh.pa.us
Backpatch: 9.5-, like ac218aa4f6

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/4c8750a9cc3402e4d8ec0b47901c2f9ca416b718

Modified Files
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src/bin/pg_upgrade/check.c | 23 ++++++++++++++---------
1 file changed, 14 insertions(+), 9 deletions(-)