Fix negative us in unix timestamp syntax

[iluuu1994]

php/php-src#7758

Let me know if there's a better way to check for the negative symbol. I'm not super familiar with re2c.

Also, tests/c/timezones_same.cpp didn't compile for me because strlen wasn't defined.

[derickr]

I've merged this (manually) into the v2020 and master branches. I will make a release of this later, after fixing a few more bugs, and then import the release with the fixes into PHP (probably not today though). Thanks!