Windows: fix compiler warning

libusb/os/threads_windows.c: In function 'usbi_cond_timedwait':
libusb/os/threads_windows.c:190:2: warning: nested extern declaration of 'epoch_time' [-Wnested-externs]
Windows: fix compiler warning

libusb/os/threads_windows.c:139:1: warning: '__inline' is not at beginning of declaration [-Wold-style-declaration]