bug#73454: mix-build-system does not support git-version output

[paul]

Dear Guix,

consider the following procedure invokation:

scheme@(guile-user)> (package-name->elixir-name "elixir-a-pkg-1.2.3")
$1 = "a_pkg"

This is the behaviour manifested when the procedure is called with a version created with the git-version procedure from (guix git-download):

scheme@(guile-user)> (package-name->elixir-name "a_pkg-0.0.0-0.e51e36e")
$1 = "a_pkg_0.0.0

while the expected behaviour would be:

scheme@(guile-user)> (package-name->elixir-name "a_pkg-0.0.0-0.e51e36e")
$1 = "a_pkg"

I'm sending a patch addressing this, thank you for your work!