BUILD: makefile: start to automatically collect CFLAGS/LDFLAGS

Now OPTIONS_CFLAGS and OPTIONS_LDFLAGS don't need to be set anymore
for options USE_xxx that set xxx_CFLAGS or xxx_LDFLAGS. These ones
will be automatically connected.

The only entry for now that was ready for this was PCRE2, so it was
adjusted so as not to append to OPTIONS_LDFLAGS anymore. More will
come later.
1 file changed