Suppress -Wextern-initializer in chromoting_lib.dlldata.c
Suppress -Wextern-initializer in chromoting_lib.dlldata.c

With the new SDK, Clang builds were failing with:

error: 'extern' variable has an initializer [-Werror,-Wextern-initializer]
PROXYFILE_LIST_START
^
C:\b\depot_tools\win_toolchain\vs2013_files\win_sdk/Include/10.0.10240.0/um\rpcproxy.h(823,39):
note: expanded from macro 'PROXYFILE_LIST_START'
    extern const ProxyFileInfo* const aProxyFileList[]    = {
                                      ^

BUG=491424, 82385
R=scottmg@chromium.org
TBR=joedow, scottmg, thakis

Review URL: https://codereview.chromium.org/1393473003 .

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#352687}

axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk