Improve build reproducibility

[diederikdehaas]

In src/umtprd.c line 147 is this code snippet:

	PRINT_MSG("Version: %s compiled %s@%s", APP_VERSION,
		  __DATE__, __TIME__);

Using __DATE__ or __TIME__ macros is bad for reproducibility.

There are ways to fix that, but that page also mentions to consider avoiding the problem in the first place.
While I can understand printing a version number or the date and/or ID of the last commit (to indicate what exact code is running), I'm not so sure whether knowing when it was compiled is useful.