gcc: Disable makenfo cause newer verisons 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 branches.

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

source-builder/config/gcc-common-1.cfg

@@ -151,6 +151,7 @@ BuildRoot: %{_tmppath}/%{name}-root-%(%{__id_u} -n)
     --enable-version-specific-runtime-libs \
     --disable-lto \
     --enable-newlib-io-c99-formats \
+    %{?disable_MAKEINFO:MAKEINFO=missing} \
     %{?with_iconv:--enable-newlib-iconv} \
     %{?with_iconv:--enable-newlib-iconv-encodings=%{_newlib_iconv_encodings}} \
     %{?with_threads:--enable-threads}%{!?with_threads:--disable-threads} \