RFA: Avoid simulator timeouts on more libstdc++ tests

[Paolo Carlini]

Hi Mark,
> This patch uses the same idiom used elsewhere in the testsuite to
> condition the size of some tests for simulators.  Running through a
> stream inserting twenty million characters in simulation can easily
> trip the 5-minute timeout, for example.
>
> OK to apply?
Yes, no problem with me. Sorry about the delay answering...

Paolo.