RFR (XS): 8141134: Remove unnecessary pragma warning(disable:4355) from GC code

[Thomas Schatzl]

Hi all,

  can I have reviews for the following change that removes some pragmas
in GC code?
With the move to newer MSVC, they are not needed any more.

CR:
https://bugs.openjdk.java.net/browse/JDK-8141134
Webrev:
http://cr.openjdk.java.net/~tschatzl/8141134/webrev/
Testing:
jprt

Thanks,
  Thomas