Make it possible to link against libstdc++ as well as libsupc++ with CMake.

Linking against libstdc++, rather than libsupc++, is probably better
for people who need to link against clients of libstdc++.  Because
libsupc++ is provided only as a static library, its globals are not
shared between the static library and the copy linked into libstdc++.
This has been found to cause at least one test failure.

This also removes a number of symbols which were multiply defined
between libstdc++ and libc++, only when linking with libstdc++.

Differential Revision: http://llvm-reviews.chandlerc.com/D1825

llvm-svn: 192075
Cr-Mirrored-From: sso://chromium.googlesource.com/_direct/external/github.com/llvm/llvm-project
Cr-Mirrored-Commit: 26dd09e57fffb23f5765ec6f7b9c0ef7b79afc82
6 files changed