Currently the vvp target emits unary real minus as `0.0 - value`.
This is not the same operation for all real values. It loses the
negative zero result for `-(+0.0)` and does not reliably flip the sign
bit for NaN values whose bits are visible through `$realtobits`.
Add `%neg/wr` and use it for unary real minus. This performs a direct
negation of the real stack value, so zero, NaN and infinity all use the
same operation as unary minus instead of a binary subtraction from zero.
Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
5311c0cd38