eval_intern.h: VAR_INITIALIZED

* eval_intern.h (VAR_INITIALIZED): macro to suppress
  maybe-uninitialized warnings by gcc 4.7 and 4.8.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@45516 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
signal.c: check stack overflow by SP

* signal.c (check_stack_overflow): raise SystemStackError if SP
  register and fault address is in the same page, on x86 linux.
  [EXPERIMENTAL]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@45517 b2dd03c8-39d4-4d8f-98ff-823fe69b080e