gcc: Disable makeinfo cause newer versions do not build gcc-4.8 docs.

Newer makeinfo tools cannot build the existing texinfo in gcc so
disable building it. This will not be fixed on the gcc branch.

Updates #3027.

rtems/config/tools/rtems-gcc-4.8-newlib-2.2.0-1.cfg

@@ -21,6 +21,8 @@
 %define with_threads 1
 %define with_plugin  0
 
+%define disable_MAKEINFO 1
+
 %ifn %{defined with_iconv}
  %define with_iconv 1
 %endif