[lld][MachO] Silence warnings about --read-workers parsing (#156608)

The parsing of the --read-workers argument v is implemented like this:

  unsigned threads = 0
  if (!llvm::to_integer(v, threads, 0) || threads < 0) {
  ...

As reported by a compiler warning, the value of the "threads < 0"
expession is never going to be true. It could only evaluate to true if v
represents a negative number, but in this case llvm::to_integer returns
false since threads is unsigned and hence the second operand of the ||
operator will not be evaluated.

This patch removes the useless || operand to silence compiler warnings.
Since I had to first find out if --read-workers=0 is valid or not (it is),
I also added a test to document the valid values for the option and I adjusted
the error message on invalid values to clearly state that 0 is valid.

0 files changed, 0 insertions, 0 deletions