uml: implement O_APPEND

The .a flags in openflags never had an implementation.
Signed-off-by: Jeff Dike <jdike@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/um/os-Linux/file.c

@@ -191,6 +191,8 @@ int os_open_file(const char *file, struct openflags flags, int mode)
 		f |= O_TRUNC;
 	if (flags.e)
 		f |= O_EXCL;
+	if (flags.a)
+		f |= O_APPEND;
 
 	fd = open64(file, f, mode);
 	if (fd < 0)