x86 hybrid: add provides for lib:libstdc++ in x86_gcc2

* this provides parity with the gcc_x86_syslibs packages, so
  that special handling isn't required for the gcc4hybrid
  builds when a recipe depends on libstdc++ (e.g. haikuwebkit)
x86: haikuwebkit 1.4.5
x86_64: haikuwebkit 1.4.5