to fix the following warning:
include/unistd.h:302:9: error: incompatible redeclaration of library function 'vfork' [-Werror,-Wincompatible-library-redeclaration]
pid_t vfork(void);
^
include/unistd.h:302:9: note: 'vfork' is a builtin with type 'int (void)'
and change 32768 to INT_MAX to match the type change
Signed-off-by: Xiang Xiao <xiaoxiang@xiaomi.com>