pgsql: Simplify/speed up assertion cross-check in ginCompressPostingLis

Simplify/speed up assertion cross-check in ginCompressPostingList().

I noticed while testing some other stuff that the CHECK_ENCODING_ROUNDTRIP
logic in ginCompressPostingList could account for over 50% of the runtime
of an INSERT with a GIN index.  While that's not relevant to production
performance, it's still kind of annoying in a debug build.  Replacing
the loop around short memcmp's with one long memcmp works just as well
and is significantly faster, at least on my machine.

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/ea7dace2aa21e79a7a8eb23c493bcd2057d9bd7e

Modified Files
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src/backend/access/gin/ginpostinglist.c | 4 +---
1 file changed, 1 insertion(+), 3 deletions(-)