[Bug sanitizer/63806] #UBSAN ignores signed char possible overflow

[y.gribov at samsung dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63806

--- Comment #5 from Yury Gribov <y.gribov at samsung dot com> ---
I've posted feature request upstream:
http://llvm.org/bugs/show_bug.cgi?id=21530