implemented make deb-build-dep. Install build dependencies listed in debian/control under Build-Depends using apt-get. Various environment variables supported.:
I didn't implement running apt-get update beforehand, because securely running apt-get update in scripts is very difficult due to unreliability of exit codes. (See: https://www.whonix.org/wiki/Dev/apt-get#Bugs) It would be best if running apt-get update was left to the user or the build script that builds the package (such as Whonix's or Qubes's build script).
Another limitation is, that it does not check the version numbers of the build dependencies. Installs those from the repository, that you apt-get updated beforehand. Isn't able to resolve or fetch packages if download from newer (such as testing) repository is required. That would require more implementation effort. I think that is also the reason, why I didn't implement make deb-build-dep any earlier.