Add the first of what will be a long line of additional error checks for invalid Mach-O files.

This is where an LC_SEGMENT load command has a fileoff field that
extends past the end of the file.

Also fix llvm-nm and llvm-size to remove the errorToErrorCode() call so error messages are printed.
And needed to update a few test cases now that they do print the error messages just a
bit differently.

llvm-svn: 277845