errors.cpp test is failing silently on gcc

[dsharlet]

The errors.cpp test is currently not passing on gcc, but it "passes" because -ferror-limit=0 is an unrecognized command line option on gcc, so it doesn't compile anything and the grep statement doesn't have a problem with it. This is annoying:

• gcc has a similar option -fmax-errors=0, but clang does not support that one. So we would need to add each option to each compiler depending on some kind of version check.
• This parameter is necessary because clang at least stops reporting errors part way through the test.