gcc needs --with-newlib in order to build correctly g++ the attached patch does that. yes, seems that *-elf is newlib in disguise...
Created attachment 104320 [details, diff] append the right option to build newlib backed g++ as said before...
unfortunately, *-elf does not always imply newlib also, you'll probably want to change gcc_do_configure() rather than gcc-compiler-configure()
Created attachment 104331 [details, diff] updated one this one maybe looks better (untested)
merged ... we'll worry about -elf toolchains w/out newlib when it comes up