Include ld-lib.exp from ctf-lib.exp

[Nick Alcock]

[Resend due to stupid typo in email address, sorry for any dups]

On 18 Feb 2021, Alan Modra said:

> It seems to me that the libctf testsuite can load ld-lib.exp rather
> than duplicating a whole lot of the infrastructure there.  Nick, do
> you see any problems with this patch?  (I don't have a CTF enabled
> compiler to fully exercise your testsuite.)

Hmm, just because the function names are the same doesn't mean the
function bodies are. I'm fairly sure I modified a bunch of these :(

... but I applied it and tested it with normal compilers,
cross-compilers, and canadian crosses and all seems well. I must have
hacked at these, then hacked them back to their original form!

So by all means install this: I'll rebase the symbol-name stuff etc on
top of it and do a quick retest before pushing.