SL-18837: Avoid stuffing build number into 32-bit int.

Even though LLVersionInfo::getBuild() already returns a 64-bit int, various
consumers assumed it could fit into 32 bits. It was especially bad to pass it
to a classic C style varargs function. Only on a little-endian CPU, and only
because it was the last argument, the damage was limited to truncation --
instead of arbitrary undefined behavior.

Where the consumer doesn't support 64-bit ints, pass as string instead.