These tests assumes availability of external symbols provided by the
C++ library, but those won't be available in case when the C++ library
is statically linked because lli itself doesn't need these.
This uses llvm-readobj -needed-libs to check if C++ library is linked as
shared library and exposes that information as a feature to lit.
Differential Revision: https://reviews.llvm.org/D41272
llvm-svn: 321981
