Until https://github.com/libopencm3/libopencm3/issues/732 has been
fixed, it's not enough to just have it in the README that you need GNU
awk. Explicitly use the "gawk" command name. This exists on (sane)
systems that have gawk as awk, and for systems that use mawk as default,
the gawk name should also exist.
This should make it significantly easier to diagnost the cause of build
problems.