Fix compile for older Linux without mmap MAP_HUGETLB

Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/os/os-linux.h b/os/os-linux.h
index 9b7ff29..e9d7cf3 100644
--- a/os/os-linux.h
+++ b/os/os-linux.h
@@ -7,6 +7,7 @@
 #include <sys/uio.h>
 #include <sys/syscall.h>
 #include <sys/vfs.h>
+#include <sys/mman.h>
 #include <unistd.h>
 #include <fcntl.h>
 #include <errno.h>
@@ -47,6 +48,10 @@
 #define FIO_USE_GENERIC_INIT_RANDOM_STATE
 #define FIO_HAVE_E4_ENG
 
+#ifdef MAP_HUGETLB
+#define FIO_HAVE_MMAP_HUGE
+#endif
+
 /*
  * Can only enable this for newer glibcs, or the header and defines are
  * missing