Build dependency on autoconf-archive when building from git

[Aleksander Morgado]

Hey!

If you're building ModemManager from git, please note that autoconf-archive (at least version 2017.03.21) is required.

There is no new build dependency required when building releases from a source tarball.

The new MM build uses AX_COMPILER_FLAGS() with lots of new compiler warnings enabled, and with -Werror enabled by default when building from git (disabled when building from tarball).

-- 
Aleksander
https://aleksander.es