Want to turn off "note" level messages in GCC

Pass the -fcompare-debug-second option to gcc.

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gcc's internal API has a diagnostic_inhibit_note() function which turns any "note:" messages off, but that is only serviceable via the unexpected -fcompare-debug-second command line switch, defined here.

Fortunately, turning notes off is its only effect, unless the -fcompare-debug or the -fdump-final-insns options are also used, which afaik are only for debugging the compiler itself.