[PATCH] [libcxx] Use pseudo-terminal in LIT tests so color output from compiler error messages is captured.

[Eric Fiselier]

>>! In D6010#9, @silvas wrote:
> FWIW, Ninja found that it wasn't tenable to use this approach. Some discussion here: https://github.com/martine/ninja/issues/174
> 
> Not sure if any of the concerns apply to lit.

Their main concern was that providing a pseudo-terminal might confuse some commands like SVN it if tries to spin up an editor.
Since we know exactly what types of command will be run this isn't a concern.

Thanks for the input.

http://reviews.llvm.org/D6010