Further reproducibility tweak

Author: dra27

configure

@@ -2490,6 +2490,9 @@ AS_CASE([$ocaml_cc_vendor,$target],
 AS_IF([test x"$bindir_to_libdir" != 'x'],
   [srcdir_abs_real="$(realpath "$srcdir_abs" 2>/dev/null)"
   AS_IF([test x"$srcdir_abs_real" = 'x'],[srcdir_abs_real="$srcdir_abs"])
+  AX_CHECK_COMPILE_FLAG([-Wa,--debug-prefix-map=old=new],
+    [internal_cflags="$internal_cflags \
+-Wa,--debug-prefix-map=$srcdir_abs=+build"], [], [$warn_error_flag])
   AX_CHECK_COMPILE_FLAG([-ffile-prefix-map=old=new],
     [internal_cflags="$internal_cflags -ffile-prefix-map=$srcdir_abs=+build"
     AS_IF([test x"$srcdir_abs_real" != x"$srcdir_abs"],