Merge libc++ 3.4 into PNaCl's branch

The localmod in CMakeLists.txt goes away -- apparently the same change
was made upstream.

A localmod in src/thread.cpp goes away since it was changed to a
cleaner "#elif defined(_SC_NPROCESSORS_ONLN)" upstream.

Conflicts:
    CMakeLists.txt
    cmake/config-ix.cmake
    include/locale
    src/locale.cpp
    src/thread.cpp

BUG=https://code.google.com/p/nativeclient/issues/detail?id=3757
TEST=PNaCl toolchain trybots