[aarch64-port-dev ] RFR: Import 2 Shenandoah build fixes

[Roman Kennke]

We found build issues on oldish compilers and i586 platform. This small
import fixes those issues.

http://cr.openjdk.java.net/~rkennke/aarch64-import-2017-03-08/webrev.00/


It is equivalent to those two patches:

http://mail.openjdk.java.net/pipermail/shenandoah-dev/2017-March/001820.html
http://mail.openjdk.java.net/pipermail/shenandoah-dev/2017-March/001822.html

Ok?

Roman