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