RFR(XS): 8211320: Aarch64: unsafe.compareAndSetByte() and unsafe.compareAndSetShort() c2 intrinsics broken with negative expected value

[Roland Westrelin]

http://cr.openjdk.java.net/~roland/8211320/webrev.00/

Intrinsics for unsafe.compareAndSetByte() and
unsafe.compareAndSetShort() don't properly deal with sign extension:
load exclusive doesn't sign extend loaded value but comparison is done
with sign extended value.

Roland.