RFR: 8144028: Use AArch64 bit-test instructions in C2

[Andrew Haley]

For some reason (oversight, I guess) we never got around to using the
bit-testing AArch64 instructions in C2.  TBZ/TBNZ are quite nice in
that they allow bit tests and branches (and tests for +ve/-ve) without
hitting the condition codes.  TST sets the condition codes based on a
set of bits in a register: it's an AND which throws the result away.

http://cr.openjdk.java.net/~aph/8144028/

Andrew.