build: Use AC_HEADER_MAJOR to find device macros

Depending on the OS/libc, device macros are defined in different
headers. This change ensures we include the right one.

sys/types.h - BSD
sys/mkdev.h - Sun
sys/sysmacros.h - glibc (Linux)

glibc currently pulls sys/sysmacros.h into sys/types.h, but this may
change in a future release.

https://sourceware.org/ml/libc-alpha/2015-11/msg00253.html

grub-core/osdep/unix/getroot.c

@@ -51,8 +51,10 @@
 #endif
 
 #include <sys/types.h>
-#if defined(HAVE_SYS_MKDEV_H)
+#if defined(MAJOR_IN_MKDEV)
 #include <sys/mkdev.h>
+#elif defined(MAJOR_IN_SYSMACROS)
+#include <sys/sysmacros.h>
 #endif
 
 #if defined(HAVE_LIBZFS) && defined(HAVE_LIBNVPAIR)