-fvisibility-inlines-hidden for x86-darwin builds

[Paolo Carlini]

A minor  nit...
> +       * libstdc++-v3/acinclude.m4:
> +         Allow OPTIMIZE_CXXFLAGS to be set by configure.host.
> +       * libstdc++-v3/configure:  Regenerated.
> +       * libstdc++-v3/configure.host:
> +         Set OPTIMIZE_CXXFLAGS to -fvisibility-inlines-hidden
> +         for x86/darwin
certainly you don't want libstdc++-v3 in the ChangeLog of libstdc++-v3 
itself (as *all* the other existing entries should also tell you ;)

Paolo.