RFR (XL): 8208669: GC changes to allow enabling -Wreorder

[Thomas Schatzl]

Hi all,

  there have been several suggestions to try to fix the Hotspot code to
allow us to enable -Wreorder in the Hotspot sources.
This should make problems due to use-before-initialization much more
obvious. 

This change fixes initializer lists for the GC directories.

There should be no change in code behavior, except for that there is
iirc one minor change that fixes the memory type of one initialization
from mtInternal to mtGC.

A later follow-up will enable -Wreorder in the makefiles.

CR:
https://bugs.openjdk.java.net/browse/JDK-8208669
Webrev:
http://cr.openjdk.java.net/~tschatzl/8208669/webrev/
Testing:
hs-tier1-4,jdk-tier1-3

Thanks,
  Thomas