Make two libstdc++ tests use -Wl,--no-enum-size-warning for ARM Linux EABI

[Paolo Carlini]

> Various g++ and gfortran tests use -Wl,--no-enum-size-warning
> for arm*-*-linux*eabi to avoid linker warnings when the test using
> -fshort-enums is linked against libraries not using -fshort-enums.
> Two libstdc++ tests need to use this option as well.  This
> patch adds the option to them; OK to commit?

Yes, it's OK, many thanks.

Paolo.