Fix typo from a couple of commits ago when I fixed a bunch of error handling.

This is what I get for submitting code without compiling it first.
Fix several build issues.

1) Don't use the system's objcopy, as that can (and did) create incompatible
files. Use the NaCl version.

2) Tolerate build failures in the Mosh main code again, due to a strange issue
on some systems being unable to link the mosh-client executable. If I could
figure out how to skip this step entirely, I would.