RFR: 8075533: Zero JVM segfaults for -version after JDK-8074552

[Severin Gehwolf]

Hi,

Could somebody please review and sponsor this patch?

The commit of JDK-8074552 broke the Zero port since it performs tests on
JVM initialization if SafeFetch32 and SafeFetchN on invalid pointers
(relying on a continuation scheme for safe fetch errors) work. Yet
performing this test correctly requires support from the signal handler
and access routines to ucontext_t which are missing for Zero.

The intent of JDK-8074552 was to improve error reporting on SEGV's.
Having this feature in Zero is less useful, since it's a C++ interpreter
only environment.

This patch disables the test and makes CanUseSafeFetch* functions return
false unconditionally for Zero JVMs so as to not produce a recursive
SEGV's during error reporting.

I've also updated test SafeFetchInErrorHandlingTest.java so it's skipped
for Zero.

bug: https://bugs.openjdk.java.net/browse/JDK-8075533
webrev:
http://cr.openjdk.java.net/~sgehwolf/webrevs/JDK-8075533/webrev.01/

Testing done: make bootcycle-images fails before this patch and passes
after for a Zero JVM on x86_64.

Thanks,
Severin