pgsql: Inline pg_popcount{32,64} into pg_popcount().

Inline pg_popcount{32,64} into pg_popcount().

On some systems, calls to pg_popcount{32,64} are indirected through
a function pointer. This commit converts pg_popcount() to a
function pointer on those systems so that we can inline the
appropriate pg_popcount{32,64} implementations into each of the
pg_popcount() implementations. Since pg_popcount() may call
pg_popcount{32,64} several times, this can significantly improve
its performance.

Suggested-by: David Rowley
Reviewed-by: David Rowley
Discussion: https://postgr.es/m/CAApHDvrb7MJRB6JuKLDEY2x_LKdFHwVbogpjZBCX547i5%2BrXOQ%40mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/cc4826dd5e52c8af7069feb49ce3cd9358fa6a6e

Modified Files
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src/include/port/pg_bitutils.h | 5 +-
src/port/pg_bitutils.c | 155 +++++++++++++++++++++++++++++++----------
2 files changed, 121 insertions(+), 39 deletions(-)