RFR(s): 8191101: Show register content in hs-err file on assert (second version)

[Thomas Stüfe]

Hi all,

May I please have reviews for this new version of this RFE.

Bug id:  https://bugs.openjdk.java.net/browse/JDK-8191101
webrev:
http://cr.openjdk.java.net/~stuefe/webrevs/8191101-show-registers-on-assert/webrev.02/webrev/

Please find old discussion thread here:
http://mail.openjdk.java.net/pipermail/hotspot-runtime-dev/2017-October/025018.html

And the first review thread from last november:
http://mail.openjdk.java.net/pipermail/hotspot-runtime-dev/2017-November/025371.html

Since then, the issue was sleeping in a pile of other issues, but I'd like
to finish this now.

For those who looked at the first version of this fix: this version is
substantially smaller than the last one. I removed all the
os::safe_memcpy() stuff and unified all the ucontext_t coding locally in
debug.cpp. That, at the costs of some very small #ifdefs, greatly reduces
the chaff this patch causes (all the copy_ucontext.. functions we had in
the os_cpu files before).

Thanks, Thomas