Put back pqsignal() as an exported libpq symbol.

Build src/common files as a library with -fPIC.

Remove pqsignal() from libpq's official exports list.

Yet further rethinking of build changes for macOS Mojave.

Still further rethinking of build changes for macOS Mojave.

Back off using -isysroot on Darwin.

MAXALIGN the target address where we store flattened value.

Test passing expanded-value representations to workers.

Don't build static libraries on Cygwin

Fix tuple_data_split() to not open a relation without any lock.

Lock relation used to generate fresh data for RMV.

Fix ALTER COLUMN TYPE to not open a relation without any lock.

Build src/common files as a library with -fPIC.

Remove pqsignal() from libpq's official exports list.

Build src/port files as a library with -fPIC, and use that in libpq.

Fix link failures due to snprintf/strerror changes.