Some compilers don't seem to recognize that clock_gettime() storing
into a struct timespec counts as initializing it, and produce "may be
used uninitialized" warnings.  Adding initializers to the structs gets
rid of the warnings, without adding enough overhead to worry about.

TESTED:
Now builds without warnings and passes tests, with 28 compilers
from GCC 4.2 and Clang 3.3 to GCC 13 and Clang 17.