This patch fixes issues with building CRuby 2.3.3 with OPT_STACK_CACHING turned on.
Note that it doesn't fully work yet. This patch does allow the core VM to build, producing the miniruby binary.
But as soon as it runs any substantial Ruby code, e.g. building the
cgi library, it ends up crashing.
The implementation in
REPLACE_ELEM and friends is probably where the remaining bug is.
It'd be nice to know what caused nobu-san to comment out
REPLACE_ELEM in the first place.
$ make install ...