This preserves user-specified LDFLAGS; we already kept user-specified
CFLAGS and CPPFLAGS. Given the shortage of complaints and the fact that
any problem caused is likely to appear at build time, no back-patch.
Dag-Erling Smørgrav and Noah Misch
Disabling auto-import requires that all libraries we use be careful about
declspecs for exported variables; and it seems they aren't. This means
that Cygwin will not give us useful info about missing PGDLLIMPORT markers;
but it's probably sufficient that MSVC and Mingw builds do.
This is expected to make it start failing when contrib modules
reference non-PGDLLIMPORT'ed global variables, as the other Windows
build methods do. Aside from the value of consistency, the underlying
implementation of this switch is pretty ugly and not really something
we want to rely on if we have to use PGDLLIMPORT anyway for MSVC.
linking both executables and shared libraries, and we add on LDFLAGS_EX when
linking executables or LDFLAGS_SL when linking shared libraries. This
provides a significantly cleaner way of dealing with link-time switches than
the former behavior. Also, make sure that the various platform-specific
%.so: %.o rules incorporate LDFLAGS and LDFLAGS_SL; most of them missed that
before. (I did not add these variables for the platforms that invoke $(LD)
directly, however. It's not clear if we can do that safely, since for the
most part we assume these variables use CC command-line syntax.)
Per gripe from Aaron Swenson and subsequent investigation.
