* vm_dump.c (backtrace): use rip in the saved context for the case
the SIGSEGV is received when the process is in userland.
Note that ip in the stack should be used if the signal is received
when it is in kernel (when it is calling syscall) [Bug #12711]
merge revision(s) 56030,56035: [Backport #12711]
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_3@56257 b2dd03c8-39d4-4d8f-98ff-823fe69b080e