Add support for unsigned time_t, to support QNX
On #18184 (moved), ryankung reports that QNX has an unsigned time_t, and therefore is unsupported by Tor.
To support unsigned time_t, someone will need to audit all our uses of time_t, and make sure that we don't do any signed/unsigned comparisons with it, that we can't underflow it, and that we don't use any negative sentinel values. Then we can revert the configuration code in #18184 (moved) that blocked compilation when time_t is unsigned.
To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information