Work around a bug in libcpp that pulls in the optional system iconv

if present instead of relying on the port we actually depend on.

The issue is that /usr/include/iconv.h has #include <stdbool.h> which
in turn, since both are included very late in the game, conflicts with
similar definintions by libcpp itself.

libstdc++ does not seem to require adjustments, so PR 161417 may not
be relevant in full.

PR:		161417

lang/gcc/files/patch-libcpp

@@ -0,0 +1,10 @@
+--- libcpp/internal.h	2012-07-30 09:24:59.000000000 +0000
++++ libcpp/internal.h	2013-09-04 00:41:26.000000000 +0000
+@@ -27,6 +27,7 @@
+ #include "cpp-id-data.h"
+ 
+ #if HAVE_ICONV
++#define __bool_true_false_are_defined
+ #include <iconv.h>
+ #else
+ #define HAVE_ICONV 0