lavu: add av_usleep() function

This function implements a delay using the first available
of the following functions:

- nanosleep()
- usleep()
- Sleep() (Windows)

The conditional #includes in time.c are simplified by including
unistd.h and windows.h whenever they are available rather than
having these lines triggered by specific functions.

Signed-off-by: Mans Rullgard <mans@mansr.com>

0 files changed, 0 insertions, 0 deletions