libtime.c: fix Windows sleep behavior

On Windows, Sleep(0) has special meaning, and is basically the equivalent of
thread_yield(). We don't want to yield the thread, but instead sleep for the
minimum amount of time possible.

Signed-off-by: Steven Noonan <steven@uplinklabs.net>
Merge branch 'master' of github.com:tycho/microbench
GNUmakefile: declare the bins and libtime as phony to let the child makes do their jobs

Signed-off-by: Steven Noonan <steven@uplinklabs.net>