a workaround for aclocal-1.8 bug

config/ac-macros/plugins.m4

@@ -750,7 +750,10 @@ dnl ---------------------------------------------------------------------------
 AC_DEFUN([_MYSQL_INCLUDE_LIST],[
  ifelse([$1], [], [], [
   m4_define([__mysql_include__],[$1])
-  sinclude($1)
+  dnl We have to use builtin(), because sinclude($1) generates an error
+  dnl "file $1 does not exists" in aclocal-1.8 - which is a bug, clearly
+  dnl violating m4 specs, and which is fixed in aclocal-1.9
+  builtin([include],$1)
   m4_undefine([__mysql_include__])
   _MYSQL_INCLUDE_LIST(m4_shift($@))
  ])