build-setup: Use a slightly later ancient timestamp for dummy files.

build-setup: Use a slightly later ancient timestamp for dummy files.

GNU Make secretly reserves extreme-valued timestamps for its own
internal purposes, and then complains about `Timestamp out of range'.
This is annoying enough; but for some reason I don't understand, at
least on Cygwin, instead of substituting its most ancient acceptable
timestamp, it uses its furthest into the future stamp with the result
that it gets stuck in a loop rebuilding makefiles.

Using the second year of the epoch seems to fix the problem.