Teach packages to find and use GMP in more cases (and possibly also other homebrew packages)

[fingolfin]

For GAP itself we taught it to look for Homebrew installed package versions in PR #5214 / commit c091cba.

We also introduced GMP_PREFIX into sysinfo.gap for packages that would like to know where GAP found GMP. This is already being used by nq (see gap-packages/nq#24).

Relevant packages (from a run of BuildPackages.sh on my mac with GAP 4.13.0):

• anupq -- see Require GMP and take GAP's GMP_PREFIX into account gap-packages/anupq#66
• CaratInterface -- see If GAP provides GMP_PREFIX, use that gap-packages/CaratInterface#35
• float -- suggested at Enhance configure to find dependencies installed via Homebrew on macOS for ARM gap-packages/float#95
• NormalizInterface -- see use GMP_PREFIX gap-packages/NormalizInterface#115

In addition, the following packages might benefit from finding Homebrew:

• CddInterface: homebrew package cddlib actually it already checks for Homebrew, nice
• ZeroMQInterface: homebrew package zmq

Off-topic, but vaguely related: passing --with-gaproot to the configure script of simpcomp leads to WARNING: unrecognized options: --with-gaproot -- perhaps that configure script can be modified to ignore that option. Or else we finally add a proper mechanism for detecting what a given package needs in order to build it, instead of "guessing" that we should run configure and make with certain arguments depending on various conditions...

[fingolfin]

This is resolved to my satisfaction. Only float remains to be changed, and I filed an issue there, so if anyone runs into this, or is interested in working on this, I can point them there. But I myself have no use for float so I won't be pushing for it there.