[Bug c/120921] gimple verifier (and gimple FE) accepts CST on LHS

[pinskia at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120921

--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Created attachment 61807
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=61807&action=edit
testcases for the invalid cases