Kernel/LibC: Implement creat with open

This allows getting rid of unnecessary SYS_CREATE. Directory creation
still has its own syscall, but I could combine it with SYS_OPEN also.

userspace/libraries/LibC/include/sys/syscall.h

@@ -56,7 +56,6 @@ __BEGIN_DECLS
 	O(SYS_POWEROFF,			poweroff)		\
 	O(SYS_CHMOD,			chmod)			\
 	O(SYS_FCHMOD,			fchmod)			\
-	O(SYS_CREATE,			create)			\
 	O(SYS_CREATE_DIR,		create_dir)		\
 	O(SYS_UNLINK,			unlink) 		\
 	O(SYS_READLINK,			readlink)		\