mkShellNoCC variant

**Is your feature request related to a problem? Please describe.** Creating devshells currently pulls in the c toolchain, which I do not need for the vast majority of my developer shells. **Describe the solution you'd like** Add a mkShellNoCC variant that people can use. **Describe alternatives you've considered** Currently I am creating an overlay that subs mkShell with mkShellNoCC but that overrides it for everything. Another alternative would be to provide devshell with a variant of pkgs with specifically overridden mkShell...