pgsql: Fix prove_installcheck to use correct paths when used with PGXS

Fix prove_installcheck to use correct paths when used with PGXS

The prove_installcheck recipe in src/Makefile.global.in was emitting
bogus paths for a couple of elements when used with PGXS. Here we create
a separate recipe for the PGXS case that does it correctly. We also take
the opportunity to make the make the file more readable by breaking up
the prove_installcheck and prove_check recipes across several lines, and
to remove the setting for REGRESS_SHLIB to src/test/recovery/Makefile,
which is the only set of tests that actually need it.

Backpatch to all live branches

Discussion: https://postgr.es/m/f2401388-936b-f4ef-a07c-a0bcc49b3300@dunslane.net

Branch
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REL_13_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/a8b564b0c9c39e8bdd6cde4245c3340f72c28899

Modified Files
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src/Makefile.global.in | 23 +++++++++++++++++++++--
src/test/recovery/Makefile | 4 ++++
2 files changed, 25 insertions(+), 2 deletions(-)