pgsql: Fix some incorrect preprocessor tests in tuplesort specializatio

Fix some incorrect preprocessor tests in tuplesort specializations

697492434 added 3 new quicksort specialization functions for common
datatypes.

That commit was not very consistent in how it would determine if we're
compiling for 32-bit or 64-bit machines. It would sometimes use
USE_FLOAT8_BYVAL and at other times check if SIZEOF_DATUM == 8. This
could cause theoretical problems due to the way USE_FLOAT8_BYVAL is now
defined based on SIZEOF_VOID_P >= 8. If pointers for some reason were
ever larger than 8-bytes then we'd end up doing 32-bit comparisons
mistakenly. Let's just always check SIZEOF_DATUM >= 8.

It also seems that ssup_datum_signed_cmp is just never used on 32-bit
builds, so let's just ifdef that out to make sure we never accidentally
use that comparison function on such machines. This also allows us to
ifdef out 1 of the 3 new specialization quicksort functions in 32-bit
builds which seems to shrink down the binary by over 4KB on my machine.

In passing, also add the missing DatumGetInt32() / DatumGetInt64() macros
in the comparison functions.

Discussion: https://postgr.es/m/CAApHDvqcQExRhtRa9hJrJB_5egs3SUfOcutP3m+3HO8A+fZTPA@mail.gmail.com
Reviewed-by: John Naylor

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/c90c16591c438e4146b1d4b9e4539f80b58845ba

Modified Files
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src/backend/access/nbtree/nbtcompare.c | 4 ++--
src/backend/utils/adt/timestamp.c | 4 ++--
src/backend/utils/sort/tuplesort.c | 21 ++++++++++++---------
src/include/utils/sortsupport.h | 2 ++
4 files changed, 18 insertions(+), 13 deletions(-)