[Bug c/87392] UBSAN behavior on left-shifting 1 into the sign bit is dependent on C standard

[joseph at codesourcery dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87392

--- Comment #7 from joseph at codesourcery dot com <joseph at codesourcery dot com> ---
The implementation-definedness of signed left shift in C90, including 
shifting into or past the sign bit (as long as the shift count isn't too 
large or negative), is stated explicitly in the response to DR#081.