The mix of CFLAGS and LDFLAGS is a bit confusing in my opinion, and

Makefile.shared was a bit overcomplicated.

Make the shell variables LDFLAGS and SHAREDFLAGS in Makefile.shared
get the values of $(CFLAGS) or $(LDFLAGS) as appropriate depending on
the value the shell variables LDCMD and SHAREDCMD get.  That leaves
much less chance of confusion, since those pairs of shell variables
always are defined together.