fix ptrdiff_t and _GNU_SOURCE detection

[m6w6/ext-psi] / m4 / posix / stddef.m4

diff --git a/m4/posix/stddef.m4 b/m4/posix/stddef.m4
index fd52d2a1c8228ac8d8a9d5fddfc351c09d2b7a2c..2c9abf28888fce399d843948b615fff78383347f 100644 (file)
--- a/m4/posix/stddef.m4
+++ b/m4/posix/stddef.m4
@@ -1,5 +1,11 @@
 PSI_CHECK_STDDEF() {
+    dnl Though, autoconf manual says "This macro is obsolescent, as current systems
+    dnl have conforming header files. New programs need not use this macro.", in fact
+    dnl AC_INCLUDES_DEFAULT still relies on STDC_HEADERS
+    AC_HEADER_STDC
+
     AC_CHECK_HEADERS(stddef.h)
+
     PSI_TYPE(ptrdiff_t, int)
     PSI_CONST(PTRDIFF_MIN, int)
     PSI_CONST(PTRDIFF_MAX, int)