llvm: Add workaround for STLport not being a full C++11 STL

Summary:
llvm checks for C++11 support in the compiler, and assumes the
STL has full C++11 support if the compiler does.
However, for the combination of gcc 4.7 and STLport, that assumption
is incorrect -- the compiler supports rvalue references just fine, but
the STL hasn't caught up yet.

Longer term, the better fix would be to fix STLport.
Signed-off-by: Bernhard Rosenkraenzer <Bernhard.Rosenkranzer@linaro.org>

cfX Note: Despite Bero's comment above, STLPort has been fixed upstream.
It hasn't been updated in over a year for tagged releases, however master is quite
a bit more modern. This is quite a chore to bring into Android, however should be
done at some point.

Test Plan: verified

Reviewers: randall.rushing, synergy

Reviewed By: synergy

Differential Revision: http://review.codefirex.com/D97