Inhermeticity in cabal2bazel ./configure step

[aherrmann]

Hazel's cabal2bazel calls the ./configure script on packages that require this step. The is done using a
call to repository_ctx.execute. It is common for configure scripts to look for tools like gcc. Since this happens in a repository rule, it has access to the regular environment (e.g. $PATH) even if --experimental_strict_action_env is set, as a quick test showed. This is an inhermiticity. E.g. this step will fail if a user does not have a global gcc installed. It could also introduce cache misses with a remote cache due to differences in setup between machines. Furthermore, if the Bazel build later on configures a different cc toolchain, say using nixpkgs_cc_configure, this could potentially cause issues due to incompatibility between the toolchains.