error.c: negative uplevel
* error.c (rb_warn_m): negative uplevel is not allowed.
[ruby-core:84568] [Bug #14262]
error.c: limit depth
* error.c (rb_warn_m): limit backtrace depth to reduce objects to
be created but not used.
error.c: prepend "warning: " always
* error.c (rb_warn_m): prepend the string "warning: " if uplevel
keyword is given, even if caller file and line information are
not available.
Fix condition in Kernel#warn when using uplevel
* It causes SEGV on `warn("foo", uplevel: 100)`.
* Found in a ruby/spec added by @andrykonchin in
https://github.com/ruby/spec/pull/605
merge revision(s) 61525,61527,63062,63650: [Backport #14846]
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_5@63819 b2dd03c8-39d4-4d8f-98ff-823fe69b080e