Selecting compiler specifically for `thumbv8m.main-none-eabi` and other `.` containing targets does not work

[datdenkikniet]

cc-rs allows users to override the compiler used for a specific target triple by setting the environment variable CC_<triple>, but for targets such as thumv8m.main-none-eabi this doesn't work as .-s are not allowed to be used in the name of an environment variable in (most?) shells, so setting e.g. CC_thumbv8m.main_none_eabi is not allowed.

It would be great if this could be supported, either by replacing the . with an _, or some other solution that allows us to actually set this environment variable.

[NobodyXu]

Does using env command works?

Replacing underscore with - sounds good but we would basically have to iterate over all variable to do that and it's not very great

[datdenkikniet]

Ah, env seems to work, yes, thanks! I hadn't thought of that. Then closing this issue should be fine, unless someone feels like adding a note to the README w.r.t. using env for some of these.

When mentioning the replacement thing, I was just thinking that it could be added to this existing function, not some big new feature.

[NobodyXu]

Yeah we can simply replace - with _ and don't have to iterate over entire env vars, so it would work.

I would welcome a PR adding that.