When using the recent dlsym() based wrapper, we are not requiring any
symbol from libmd, as we resolve those dynamically at run-time. We were
ending up linking against libmd because in another part of the code we
require (depending on the architecture) the SHA512 functions for the
getentropy() local implementation. But that function might be provided
by the system libc on some systems, which means we end up not linking
against libmd at all.
To solve this we go back to the previous simpler solution of linking
directly, which had the main drawback of then making programs fail to
link when not specifying -lmd (on platforms that need it). And then
switch the .so link point from a symlink to a linker script, so that we
can inject the -lmd library as-needed. This is similar to what glibc is
doing.
Fixes: commit 31f034e386
Detect as many warnings as possible during configure and enable them
if the user did not supply any, so that any such problem can be spotted
and fixed.
