RFR: 8075045: AARCH64: Stack banging should use store rather than load

[Andrew Haley]

At present, stack banging uses a load rather than a store instruction.
We have discovered that on some AArch64 implementations a store
performs considerably better but on no implementation is it worse.
Therefore, at least for the time being, all stack bangs should use a store.

http://cr.openjdk.java.net/~aph/8075045/

Andrew.