pgsql: Further portability tweaks for float4/float8 hash functions.

Further portability tweaks for float4/float8 hash functions.

Attempting to make hashfloat4() look as much as possible like
hashfloat8(), I'd figured I could replace NaNs with get_float4_nan()
before widening to float8. However, results from protosciurus
and topminnow show that on some platforms that produces a different
bit-pattern from get_float8_nan(), breaking the intent of ce773f230.
Rearrange so that we use the result of get_float8_nan() for all NaN
cases. As before, back-patch.

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/b30cc0fd6d5d96c63037824c286cec561e092b6f

Modified Files
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src/backend/access/hash/hashfunc.c | 22 ++++++++++++----------
1 file changed, 12 insertions(+), 10 deletions(-)