autoconf: check endian.h include path

Introduce an autoconf macro to check for the include path of certain
headers that can be different between OSes.

Use such macro to find the correct path for the endian.h header, and
modify the users of endian.h to use the output of such check.

Suggested-by: Ian Jackson <iwj@xenproject.org>
Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Reviewed-by: Ian Jackson <iwj@xenproject.org>
Release-Acked-by: Ian Jackson <iwj@xenproject.org>

m4/header.m4

@@ -0,0 +1,13 @@
+AC_DEFUN([AX_FIND_HEADER], [
+ax_found=0
+m4_foreach_w([header], $2, [
+    AS_IF([test "$ax_found" = "0"], [
+        AC_CHECK_HEADER(header, [
+            AC_DEFINE($1, [<header>], [Header path for $1])
+            ax_found=1])
+    ])
+])
+AS_IF([test "$ax_found" = "0"], [
+    AC_MSG_ERROR([No header found from list $2])
+])
+])

tools/configure.ac

@@ -74,6 +74,7 @@ m4_include([../m4/ax_compare_version.m4])
 m4_include([../m4/paths.m4])
 m4_include([../m4/systemd.m4])
 m4_include([../m4/golang.m4])
+m4_include([../m4/header.m4])
 
 AX_XEN_EXPAND_CONFIG()
 
@@ -517,4 +518,6 @@ AC_ARG_ENABLE([pvshim],
 ])
 AC_SUBST(pvshim)
 
+AX_FIND_HEADER([INCLUDE_ENDIAN_H], [endian.h sys/endian.h])
+
 AC_OUTPUT()

tools/libs/guest/xg_dom_decompress_unsafe_lzo1x.c

@@ -1,7 +1,7 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <inttypes.h>
-#include <endian.h>
+#include INCLUDE_ENDIAN_H
 #include <stdint.h>
 
 #include "xg_private.h"

tools/libs/guest/xg_dom_decompress_unsafe_xz.c

@@ -1,5 +1,5 @@
 #include <stdio.h>
-#include <endian.h>
+#include INCLUDE_ENDIAN_H
 #include <stdlib.h>
 #include <stddef.h>
 #include <stdint.h>

tools/libs/guest/xg_dom_decompress_unsafe_zstd.c

@@ -1,5 +1,5 @@
 #include <stdio.h>
-#include <endian.h>
+#include INCLUDE_ENDIAN_H
 #include <stdlib.h>
 #include <stddef.h>
 #include <stdint.h>

tools/xenstore/include/xenstore_state.h

@@ -21,11 +21,7 @@
 #ifndef XENSTORE_STATE_H
 #define XENSTORE_STATE_H
 
-#if defined(__FreeBSD__) || defined(__NetBSD__)
+#include INCLUDE_ENDIAN_H
-#include <sys/endian.h>
-#else
-#include <endian.h>
-#endif
 #include <sys/types.h>
 
 #ifndef htobe32