[Bug c/78768] -Walloca-larger-than and -Wformat-length warnings disabled by -flto

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78768

--- Comment #4 from Martin Sebor <msebor at gcc dot gnu.org> ---
Patch to add LTO to the set of languages these options are enabled for posted
for review:
https://gcc.gnu.org/ml/gcc-patches/2017-01/msg00658.html