signal.c: improve stack overflow check
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@56907 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
signal.c: improve stack overflow check
segfault a stack overflow when the fault address is between SP
and BP.
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@56907 b2dd03c8-39d4-4d8f-98ff-823fe69b080e