7c6a3e4a0b wound up always forcing the
usage of gettimeofday (even when the more accurate CLOCK_MONOTONIC was
available) because the define to indicate its availability is in
config.h which wasn't included.
Fix this by including config.h, correct the misnamed variable in the
CLOCK_MONOTONIC branch and rename VERSION to PERF_VERSION to avoid the
naming conflict.
831b222917