um: falloc.h needs to be directly included for older libc

When building UML with glibc 2.17 installed, compilation
of arch/um/os-Linux/file.c fails due to failure to find
FALLOC_FL_PUNCH_HOLE and FALLOC_FL_KEEP_SIZE definitions.

It appears that /usr/include/bits/fcntl-linux.h (indirectly
included by /usr/include/fcntl.h) does not include falloc.h
with an older glibc, whereas a more up-to-date version
does.

Adding the direct include to file.c resolves the issue
and does not cause problems for more recent glibc.

Fixes: 50109b5 ("um: Add support for DISCARD in the UBD Driver")
Cc: Brendan Higgins <[email protected]>
Signed-off-by: Alan Maguire <[email protected]>
Reviewed-by: Brendan Higgins <[email protected]>
Acked-By: Anton Ivanov <[email protected]>
Signed-off-by: Richard Weinberger <[email protected]>

Author: alan-maguire

arch/um/os-Linux/file.c

@@ -8,6 +8,7 @@
 #include <errno.h>
 #include <fcntl.h>
 #include <signal.h>
+#include <linux/falloc.h>
 #include <sys/ioctl.h>
 #include <sys/mount.h>
 #include <sys/socket.h>