Suppress new ignored-attributes warning

In file included from external/icu/icu4c/source/common/putil.cpp:68:
external/icu/icu4c/source/common/umutex.h:52:17: error: 'dllexport' attribute ignored on explicit instantiation definition [-Werror,-Wignored-attributes]
template struct U_COMMON_API std::atomic<int32_t>;
                ^
external/icu/icu4c/source/common/unicode/utypes.h:316:24: note: expanded from macro 'U_COMMON_API'
#define U_COMMON_API   U_EXPORT
                       ^
external/icu/icu4c/source/common/unicode/platform.h:790:32: note: expanded from macro 'U_EXPORT'
#   define U_EXPORT __declspec(dllexport)
                               ^
1 error generated.

Test: Build
Bug: 131328001
Change-Id: Ia8d8e2325141eb0e684c4ec0c5627812f49f43e2
1 file changed