Replace some '@%:@' quadigraphs by its actual representation '#'.

This quadigraph used before a C preprocessor 'define' directive could
be fooling M4, when processing this file, and make it think that the
line contains a pure M4 'define' macro.

m4/reentrant.m4

@@ -354,9 +354,9 @@ AC_DEFUN([CARES_CONFIGURE_FROM_NOW_ON_WITH_REENTRANT], [
 AC_DEFINE(NEED_REENTRANT, 1,
   [Define to 1 if _REENTRANT preprocessor symbol must be defined.])
 cat >>confdefs.h <<_ACEOF
-[@%:@ifndef _REENTRANT
-@%:@ define _REENTRANT
-@%:@endif]
+[#ifndef _REENTRANT
+# define _REENTRANT
+#endif]
 _ACEOF
 ])