Avoid unicode in NIF compilation errors in unit tests

Set LC_ALL to C to avoid unicode characters in the any error messages
from the compiler.
Handle unicode in NIF compilation errors in unit tests

If there are any NIF compilation errors in the unit tests, print them
with ~ts instead of ~s, since the latter form crashes with badarg for
unicode text.
Allow ERL and ERLC override
Merge branch 'egcrowe/improve-make'
Prepare for 3.14.0