Added --llvm-repository and --llvm-version

[mulle-nat]

The idea is that people with their own clang fork can specify their version and repository and get it build with llvm-mingw. This is a self serving patch request, because that's just what I needed. :)

[mstorsjo]

You can already set the LLVM version, e.g. as LLVM_VERSION=<foo> ./build-all.sh. It's not quite as well presented as an actual option, but it's also a kinda fringe usecase.

I'd be ok with switching the LLVM repo url to use the same pattern for default initialization if not set by the caller (see line 19 in build-llvm.sh), but I'm not sure if I'd want to add these extra explicit options for it.

[mulle-nat]

Dude its not a biggy for me. Feel free to drop the pull request. I can live with a fork :)

[mstorsjo]

Dude its not a biggy for me. Feel free to drop the pull request. I can live with a fork :)

Well if we'd just keep LLVM_VERSION as it is, and add an LLVM_REPOSITORY variable in the same sense, we could totally merge this, and you wouldn't need to keep differences in this repo at least :-)

[mulle-nat]

Sounds fine to me :)