Adapt jlibtool to work with BIND's build system

[fanf2]

Greetings! Especially to whoever drives your twitter account and responded to my wittering over there :-)

I thought it might be worth trying to use jlibtool to make BIND build faster. I got it to work with a bit of hacking. On my MacBook Pro M1 Pro (sic) it reduces the time of make -j all (after make clean) from 22.1s to 16.8s. It fairly consistently saves about 5s, to build about 460 .c files. (BIND and FreeRADIUS are remarkably similar in size.) A 20+% speedup is pretty nice, thanks for maintaining jlibtool!

BIND's build system was revamped a few years ago to use autotools in modern style, so I guess that other autotools builds could also benefit from these patches since my test case is not too idiosyncratic. Some of these patches are incidental cleanups that I found on the way.

The main changes here are

• discard the --tag option instead of passing it through
• relax the library version number format
• spawn commands directly instead of via the shell (saves me about 0.5s)
• do not try to link a shared library when jlibtool is not given a -rpath option

That last change is the one I am least sure about. There's a fair amount of Mac-related shenanigans in link_fixup() which I tripped over, but the change I settled on is not specific to MacOS. However I am not sure if it is cromulent to change cmd->output at a relatively late stage, or if jlibtool should have made a different decision earlier.

Anyway, I hope these changes are OK; let me know if I need to change or improve anything!

[fanf2]

Oops, looks like my no-shell hack broke the FreeRADIUS build, so I have dropped that patch from my branch.

(I think the 0.5s improvement was probably measurement error because the timing is very noisy; probably 0.1s is more like it, so it isn't really worth the effort...)

[alandekok]

I've merged these commits manually. GitHub offers a "squash and merge" option, which is less useful.