RFR(S) 8055007: NMT2: emptyStack missing in minimal build

[Zhengyu Gu]

Based on early comments, changed emptyStack global object to static 
member of NativeCallStack. Also made it available to minimal VM.


Bug:https://bugs.openjdk.java.net/browse/JDK-8055007 
<https://bugs.openjdk.java.net/browse/JDK-8055007>
Webrev: http://cr.openjdk.java.net/~zgu/8055007/webrev.00/ 
<http://cr.openjdk.java.net/%7Ezgu/8055007/webrev.00/>

Test:
  -  Built minimal vm, and ran "./hotspot -version"

  output:
   java version "1.9.0-ea"
   Java(TM) SE Runtime Environment (build 1.9.0-ea-b26)
   Java HotSpot(TM) Minimal VM (build 1.9.0-internal, mixed mode)

   - JPRT
   - vm.quick.testlist on Linux x64 and Solaris Sparcv9

Thanks,

-Zhengyu