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Control Warnings: `-W', `--warn', `--no-warn', `--fatal-warnings'

   `as' should never give a warning or error message when assembling
compiler output.  But programs written by people often cause `as' to
give a warning that a particular assumption was made.  All such
warnings are directed to the standard error file.
   If you use the `-W' and `--no-warn' options, no warnings are issued.
This only affects the warning messages: it does not change any
particular of how `as' assembles your file.  Errors, which stop the
assembly, are still reported.
   If you use the `--fatal-warnings' option, `as' considers files that
generate warnings to be in error.
   You can switch these options off again by specifying `--warn', which
causes warnings to be output as usual.