Otherwise you get:

In file included from src/IceGlobalContext.cpp:21:
In file included from src/IceCfg.h:21:
src/IceGlobalContext.h:257:44: error: variable 'TLS' is uninitialized when used within its own initialization [-Werror,-Wuninitialized]
    ThreadContext *TLS = ICE_TLS_GET_FIELD(TLS);
                   ~~~                     ^~~
src/IceTLS.h:95:39: note: expanded from macro 'ICE_TLS_GET_FIELD'
                                      ^
So rename the local var to Tls.

BUG=none
R=stichnot@chromium.org

Review URL: https://codereview.chromium.org/1030793002