pgsql: Fix link error for test_radixtree module on Windows

Fix link error for test_radixtree module on Windows

Add PGDLLIMPORT to pg_popcount32/64. In passing, fix a typo.

Diagnosis by Masahiko Sawada, patch by David Rowley

Per buildfarm members drongo and fairywren

Discussion: https://postgr.es/m/CAD21AoAMm1mQd%3Dw4PrfrKK%3DOMP8j8%3D7ntJRPF8%2B%3D10iUuvwiCA%40mail.gmail.com
Discussion: https://postgr.es/m/CAApHDvov7724UrD1Ug0D1eV%2B9Pd_x5VEQmw-6HVG9w1WdCxXPA%40mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/ab6ae6260372074de71805cb7fd54d55d2da994d

Modified Files
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src/include/port/pg_bitutils.h                   | 4 ++--
src/test/modules/test_radixtree/test_radixtree.c | 2 +-
2 files changed, 3 insertions(+), 3 deletions(-)