build-toolchain.sh should include isl

[Jan200101]

build-toolchain.sh currently sets up the gcc build to include gmp, mpc and mpfr but not isl which is also a dependency of gcc.

[Jan200101]

related issue #312

[rasky]

I thought isl is optional?

[networkfusion]

@Jan200101 Are you using WSL1 or WSL2 (given you have linked that issue)?!

[Jan200101]

I thought isl is optional?

Doesn't seem to be from looking at the gcc configure.ac script.
https://gcc.gnu.org/install/prerequisites.html also doesn't mention it as optional (though it doesn't mention anything being optional, just that they could be).

On a CI runner I ran into Unable to find a usable isl. See config.log for details.

Are you using WSL1 or WSL2 (given you have linked that issue)?!

Not using WSL at all, this occured on a Fedora based runner.
I linked the issue because it ran into the same error message

[rasky]

OK I think the reason I've never realized this is that isl is a dependency also of gmp. So if you install gmp through a package manager, you get isl. And even if you uninstall it to test the gmp source build, there's still isl in your system :)

I guess we need to amend the script to also download and copy isl then.

[rasky]

This has been implemented for Mac for now.