meson: Export all libcommon functions in Windows builds

meson: Export all libcommon functions in Windows builds

This fixes "unresolved external symbol" errors with extensions that
use functions from libpgport that need special CFLAGS to
compile. Currently, that includes the CRC-32 functions.

Commit 2571c1d5cc did this for libcommon, but I missed that libpqport
has the same issue.

Reported-by: Tom Lane
Backpatch-through: 16, where Meson was introduced
Discussion: https://www.postgresql.org/message-id/CAOdR5yF0krWrxycA04rgUKCgKugRvGWzzGLAhDZ9bzNv8g0Lag@mail.gmail.com