--build-from-source does not work for riscv-gcc formula

[dmzimmerman]

brew reinstall --build-from-source riscv-gcc does not complete; instead, it hangs at "Checking out branch master" (probably because the riscv-gcc repository has no master branch, and Homebrew defaults to checking out master).

[dmzimmerman]

Actually, I believe I am mistaken here; it does complete, it just takes a very, very long time with no progress indication - the naming of the formula confused me into thinking that it was building from the riscv-gcc repository, when in fact it is building from the riscv-gnu-toolchain repository (which has many subrepositories, and takes a lot longer). It might be a reasonable idea to rename this formula to riscv-gnu-toolchain to avoid such confusion.

[sbeamer]

This is a reasonable suggestion, and there is no reason it has the name riscv-gcc other than it was the name of the repo before it was renamed to riscv-gnu-toolchain.

[dmzimmerman]

Updating the reference in the documentation is good (thanks!), but probably renaming the actual formula to riscv-gnu-toolchain would be better as far as clarity going forward.