Add an cross include path for ARM to work around clang bug 22937.

Add an cross include path for ARM to work around clang bug 22937.

Clang appears to be missing an include path to find
bits/c++config.h so we were unable to compile the
unsandboxed c++ based cross tests and link against the
subzero unsandboxed ARM object files.

Work around this for now by finding and including the
missing path.

Turn on a few ARM cross tests that should be working
(mem_intrin and test_strengthreduce -- though the
strength-reduction isn't done for ARM). The test_bitmanip
still fails, because under Om1 we overflow the stack offset
and need to materialize that offset with a register first.

Update a few other references that still say x8632.

BUG= https://code.google.com/p/nativeclient/issues/detail?id=4076
R=jpp@chromium.org, stichnot@chromium.org

Review URL: https://codereview.chromium.org/1232183002 .