Eliminate more symbols multiply defined between libsupc++ and libc++.

The remaining multiple definitions were flushed out by attempting to
link libsupc++ and libc++ into the same executable with --whole-archive,
e.g.

clang++ -I../llvm/projects/libcxx/include -nodefaultlibs -Wl,--whole-archive lib/libc++.a /usr/lib/gcc/x86_64-linux-gnu/4.6/libsupc++.a -Wl,--no-whole-archive -lgcc -lgcc_s -lc -lpthread -lrt

(The same technique was used to flush out multiple definitions in
libstdc++.)

Differential Revision: http://llvm-reviews.chandlerc.com/D1824

llvm-svn: 192074