RFR: 8241438: Move IntelJccErratum mitigation code to platform-specific code

[Erik Österlund]

Hi,

There is some platform-specific code in PhaseOutput that deals with the 
IntelJccErratum mitigation,
which is ifdef:ed in shared code. It should move to platform-specific code.

This patch exposes the iteration state of PhaseOutput, which allows 
hiding the Intel-specific code
completely in x86-specific files.

Webrev:
http://cr.openjdk.java.net/~eosterlund/8241438/webrev.00/

Bug:
https://bugs.openjdk.java.net/browse/JDK-8241438

Thanks,
/Erik