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
diff --git a/icu4c/source/common/Android.bp b/icu4c/source/common/Android.bp
index 8b553bc..a2c8cbb 100644
--- a/icu4c/source/common/Android.bp
+++ b/icu4c/source/common/Android.bp
@@ -37,6 +37,7 @@
         "-Wno-missing-field-initializers",
         "-Wno-sign-compare",
         "-Wno-deprecated-declarations",
+        "-Wno-ignored-attributes",
     ],
 
     cppflags: [