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>

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()