+ [rm -rf conftestd1 conftestd2
+ mkdir conftestd1 conftestd2
+ cat <<EOF > conftestd1/conftest.h
+#define DEFINED_IN_CONFTESTD1
+#include_next <conftest.h>
+#ifdef DEFINED_IN_CONFTESTD2
+int foo;
+#else
+#error "include_next doesn't work"
+#endif
+EOF
+ cat <<EOF > conftestd2/conftest.h
+#ifndef DEFINED_IN_CONFTESTD1
+#error "include_next test doesn't work"
+#endif
+#define DEFINED_IN_CONFTESTD2
+EOF
+ save_CPPFLAGS="$CPPFLAGS"
+ CPPFLAGS="$CPPFLAGS -Iconftestd1 -Iconftestd2"
+ AC_COMPILE_IFELSE([#include <conftest.h>],