[s390] [jdk8] Increase javac default stack size for s390x zero

On JDK8, we run s390x as zero.

s390x, by default, needs a lot of stack space for C++ frames since the s390x ABI requires a 160-byte register save area to be prepared at all call sites. That affects zero in particular since the C++ interpreter builds up C-frames for Java frames; furthermore, it affects javac since it uses a lot of recursions.

This causes several javac TCK tests to fail with SOE, particularly stmt33002mxxx.

To pass TCK, the default stack size of javac should be increased to 2M for s390 on JDK 8.