Re: Too late!
"Anything else can be patched by changing time_t to unsigned."
Tried, tested, and proven.
For some applications. Not all. Go read the archives of comp.lang.c from 1999 - people identified many codebases that relied on treating a time_t as a signed int and getting a positive value. Typically that had to do with comparing for <0 rather than (time_t)-1 to check for errors.
But who am I to disagree with the Reg readership hivemind? As usual, it knows all.