+ [rm -rf conftestd1a conftestd1b conftestd2
+ mkdir conftestd1a conftestd1b conftestd2
+ dnl IBM C 9.0, 10.1 (original versions, prior to the 2009-01 updates) on
+ dnl AIX 6.1 support include_next when used as first preprocessor directive
+ dnl in a file, but not when preceded by another include directive. Check
+ dnl for this bug by including <stdio.h>.
+ dnl Additionally, with this same compiler, include_next is a no-op when
+ dnl used in a header file that was included by specifying its absolute
+ dnl file name. Despite these two bugs, include_next is used in the
+ dnl compiler's <math.h>. By virtue of the second bug, we need to use
+ dnl include_next as well in this case.
+ cat <<EOF > conftestd1a/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 > conftestd1b/conftest.h
+#define DEFINED_IN_CONFTESTD1
+#include <stdio.h>
+#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
+ gl_save_CPPFLAGS="$CPPFLAGS"
+ CPPFLAGS="$gl_save_CPPFLAGS -Iconftestd1b -Iconftestd2"
+dnl We intentionally avoid using AC_LANG_SOURCE here.
+ AC_COMPILE_IFELSE([AC_LANG_DEFINES_PROVIDED[#include <conftest.h>]],