Rewrite gac to not use libtool

[fingolfin]

This is incomplete work in progress, but I wanted to post it here
just for reference. I'll hopefully be able to resume work on this
in the not so distant future.

For now, things to be done include:

• actually make the revised gac work in all situations
• add a test which builds the new MockPkg kernel extension and verifies it works (this should be completed and merged before this PR, so that we can verify things keep working)
• add a test which does make install and then runs the test suite using that installed version (including the mockpkg kernel extension test mentioned above) not necessary here, this is to be done for the make install PR Add support for make install (still somewhat experimental, but ready to be tested by downstream packagers) #4492

Resolves #4172
Resolves #1307

[fingolfin]

Compiling NormalizInterface, we get:

gcc -m32 -m32 --coverage -L/home/runner/work/gap/gap -shared -m32 -lstdc++ -R/home/runner/work/gap/gap/pkg/NormalizInterface-1.3.0/NormalizInstallDir/lib -L/home/runner/work/gap/gap/pkg/NormalizInterface-1.3.0/NormalizInstallDir/lib -lnormaliz -o bin/x86_64-pc-linux-gnu-default32-kv8/NormalizInterface.so gen/src/normaliz.lo
gcc: error: unrecognized command line option ‘-R’

That's something to be fixed in NormalizInterface (not quite sure how yet, but one step after the other)

UPDATE: seems libtool turns -R/foo/bar into -Wl,-rpath -Wl,/foo/bar on Linux, so perhaps I should just teach gac to do that, too...

UPDATE2: on macOS, it seems to be ignored?

UPDATE3: ... though on macOS, one can still path the -rpath flag -- it has a different meaning, though, but that is irrelevant here. Point is, that would make for a very simple implementation.... I have no idea what it does on e.g. OpenBSD, FreeBSD, ... but I am not sure I care overly much right now...

UPDATE4: actually the latest NormalizInterface 1.3.1 won't use -R anymore so I'll just wait for the package distro to be updated again :-)

[fingolfin]

Two failures left, both in building packages:

1. NormalizInterface dies with the following error; this is already fixed in the latest release of the package (for unrelated reasons)

gcc -o bin/x86_64-pc-linux-gnu-default64-kv8/NormalizInterface.so gen/src/normaliz.lo --coverage -shared -lstdc++ -R/home/runner/work/gap/gap/pkg/NormalizInterface-1.3.0/NormalizInstallDir/lib -L/home/runner/work/gap/gap/pkg/NormalizInterface-1.3.0/NormalizInstallDir/lib -lnormaliz
  gcc: error: unrecognized command line option ‘-R’
  Makefile.gappkg:131: recipe for target 'bin/x86_64-pc-linux-gnu-default64-kv8/NormalizInterface.so' failed

2. nq fails because it relies on getting the compiler/linker flags for accessing GMP from GAP. I'll think about how to best address this...

[fingolfin]

nq 2.5.8 resolved those issues! Sadly testpackages tests still fail because NormalizInterface crashes. Hmm. Maybe related to gap-system/PackageDistro#285 ? Anyway, I've next tried to build it using libnormaliz-dev instead, but that doesn't work in ubuntu-18.04. So I switched to ubuntu-latest -- which is fine, except that they've dropped 32bit support there sigh

[fingolfin]

I'll try and see if I can get this ready for GAP 4.12.0.

Perhaps @ChrisJefferson has an idea why NormalizInterface might crash?

[fingolfin]

@ChrisJefferson this is finally ready for review and merging -- with the latest NormalizInterface update, that last blocker has been removed! Also, the patch is now fairly small, as I already got most of the changes merged separately.