[Bug middle-end/111659] document that -Wstrict-flex-arrays depends on -ftree-vrp

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111659

--- Comment #7 from sandra at gcc dot gnu.org ---
You're right, I did garble the description of the option in my previous patch. 
Will fix.