fec: enable building on Mac

Enable the host libfec and the fec tool to be built on Mac with the
help of <utils/Compat.h>.

Change-Id: I5e7c9fac11f4a00814bad92734e703ec8dc22dc9
diff --git a/libfec/fec_open.cpp b/libfec/fec_open.cpp
index f25aa7f..1923406 100644
--- a/libfec/fec_open.cpp
+++ b/libfec/fec_open.cpp
@@ -14,7 +14,6 @@
  * limitations under the License.
  */
 
-#include <linux/fs.h>
 #include <stdlib.h>
 #include <sys/ioctl.h>
 #include <sys/stat.h>
@@ -24,6 +23,14 @@
     #include <ext4_sb.h>
 }
 
+#if defined(__linux__)
+    #include <linux/fs.h>
+#elif defined(__APPLE__)
+    #include <sys/disk.h>
+    #define BLKGETSIZE64 DKIOCGETBLOCKCOUNT
+    #define fdatasync(fd) fcntl((fd), F_FULLFSYNC)
+#endif
+
 #include "fec_private.h"
 
 /* used by `find_offset'; returns metadata size for a file size `size' and