We have recently changed the compiler to emit a warning
for each undefined function with a generic error at the
end saying the module could not be defined.
Unfortunately, some tools like IDEs and Phoenix Reloader
give higher priority to errors over warnings, which means
an error would be shown but without any actionable
information.
This commit changes it so the first undefined function is
an error and all following ones are warnings.
José Valim
8b82564ebd