pgsql: Backport: Add inline murmurhash32(uint32) function.

Backport: Add inline murmurhash32(uint32) function.

The function already existed in tidbitmap.c but more users requiring
fast hashing of 32bit ints are coming up.

Author: Andres Freund
Discussion:
    https://postgr.es/m/20170914061207.zxotvyopetm7lrrp@alap3.anarazel.de
    https://postgr.es/m/15ae5ae2-bc74-ebef-f9d6-34b16423cc04@blackducksoftware.com
Original-Commit: 791961f59b792fbd4f0a992d3ccab47298e79103

Branch
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REL_10_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/c0fda304df276606e6b3c9ce5c63c187fe775602

Modified Files
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src/backend/nodes/tidbitmap.c | 20 ++------------------
src/include/utils/hashutils.h | 27 +++++++++++++++++++++++++++
2 files changed, 29 insertions(+), 18 deletions(-)