west: commands: build: Specify source dir without a flag

In order to simplify the usage of `west build`, take a positional
argument with the source directory instead of requiring the `-s,
--source-dir` flag. This makes it easier and quicker to invoke west when
building, as well as being consistent with CMake.

Signed-off-by: Carles Cufi <carles.cufi@nordicsemi.no>
4 files changed