[Bug target/104525] timeout on signed overflow at O0 fwrapv

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104525

--- Comment #1 from Jiu Fu Guo <guojiufu at gcc dot gnu.org> ---
with "-fsigned-char", the case run ok. 
When 'char' is treated as 'unsigned': "c != -4" would not be true is any value
of 'c'.
So, this PR would be invalid.