libdevmapper.h: make this include file standard-compliant

This file may be included by other programs, so it should be compliant
with the C standard.

* use __linux__ instead of linux - __linux__ is always defined, linux is
  not defined when gcc runs in standard-compliant mode (with -std=c89 or
  -std=c99) because the C standard doesn't allow polluting namespace
  with arbitrary defines.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>

---
 libdm/libdevmapper.h |   10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

Index: LVM2.2.02.98/libdm/libdevmapper.h
===================================================================
--- LVM2.2.02.98.orig/libdm/libdevmapper.h	2013-03-16 02:10:56.000000000 +0100
+++ LVM2.2.02.98/libdm/libdevmapper.h	2013-03-16 02:20:51.000000000 +0100
@@ -21,7 +21,7 @@
 #include <sys/types.h>
 #include <sys/stat.h>
 
-#ifdef linux
+#ifdef __linux__
 #  include <linux/types.h>
 #endif