Defining _XOPEN_SOURCE on its own hides definitions in other headers
(which is already mentioned in upstream commit f49941a). One way to
deal with this is to define _DEFAULT_SOURCE in addition to
_XOPEN_SOURCE, which is what this commit implements.

This is one way to avoid an implicit function declaration in the
built-in mmap test that autoconf provides. It includes <unistd.h> and
expects that to provide a declaration of getpagesize because the
earlier check for HAVE_GETPAGESIZE succeeded. Without addressing the
implicit function declaration, the outcome of this check will change
with future compilers which no longer support them by default.

Submitted upstream: <https://github.com/baszoetekouw/pinfo/pull/35>


diff --git a/macros/wchar.m4 b/macros/wchar.m4
index 2dc3d3a940f6c6fd..a7d6e967024df594 100644
--- a/macros/wchar.m4
+++ b/macros/wchar.m4
@@ -78,7 +78,8 @@ AC_DEFUN([AC_CHECK_WCHAR],[
 		then
 			AC_COMPILE_IFELSE([
 				AC_LANG_PROGRAM( 
-					[[ 
+					[[
+						#define _DEFAULT_SOURCE
 						#define _XOPEN_SOURCE 600
 						#include <wchar.h> 
 					]],
@@ -87,7 +88,7 @@ AC_DEFUN([AC_CHECK_WCHAR],[
 				[
 					dnl if found, set variables and print result
 					have_wcwidth=true
-					wchar_flags="$wchar_flags -D_XOPEN_SOURCE=600"
+					wchar_flags="$wchar_flags -D_DEFAULT_SOURCE -D_XOPEN_SOURCE=600"
 					AC_MSG_RESULT([with -D_XOPEN_SOURCE=600])
 				],
 				[ ]