When an arithmetic instruction generates an invalid operation
exception or a divide by zero exception, and that exception is enabled
in the FPSCR, the writing of the result to the destination register
should be suppressed, leaving whatever value was last written in the
destination. Add a check that this occurs correctly, for the cases of
square root of a negative number (invalid operation exception) and
division by zero (zero divide exception).
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
