Implement mch_delay on top of libuv

Needed to temporarily move two static variables from os_unix.c to 'globals.h'
as those are shared by other functions still in os_unix.

src/os_unix.h

@@ -4,7 +4,6 @@
 void mch_write(char_u *s, int len);
 int mch_inchar(char_u *buf, int maxlen, long wtime, int tb_change_cnt);
 int mch_char_avail(void);
-void mch_delay(long msec, int ignoreinput);
 void mch_startjmp(void);
 void mch_endjmp(void);
 void mch_didjmp(void);