Work around missing __mulodi4() on ARMv7 + Clang builds.

gyp/dng_sdk.gyp

 # Copyright 2016 Google Inc.
 #
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 # The Adobe DNG SDK, an API for reading and writing DNG files.
 {
 'variables': {
   'other_cflags': [
     '-DqDNGBigEndian=0',
     '-DqDNGReportErrors=0',
@@ skipping 125 matching lines @@
             '/DqDNGUseXMP#0',
             '/DqDNGValidate#0',
             '/DqDNGValidateTarget#1',
           ],
         },
       },
     }],
     ['skia_os != "linux"', {
       'sources': ['<@(headers)'],
     }],
+    ['skia_arch_type == "arm" and skia_clang_build', {
+      # DNG SDK uses __builtin_smulll_overflow() to detect 64x64 bit multiply overflow.
+      # On ARMv7, Clang implements this with __mulodi4() in libclang_rt.
+      # I can't quite figure out how to link that here, so instead here's a shim for
+      # __builtin_smulll_overflow() that multiplies normally assuming no overflow.
+      # Tracked in b/29412086.
+      'defines': [ '__builtin_smulll_overflow(x,y,p)=(*(p)=(x)*(y), false)' ],
+    }],
   ],
   'dependencies': [
     'libjpeg-turbo-selector.gyp:libjpeg-turbo-selector',
     'zlib.gyp:zlib',
   ],
   'include_dirs': [
     '../third_party/externals/dng_sdk/source',
     '../third_party/externals/libjpeg-turbo',
   ],
   'direct_dependent_settings': {
@@ skipping 62 matching lines @@
     '../third_party/externals/dng_sdk/source/dng_temperature.cpp',
     '../third_party/externals/dng_sdk/source/dng_tile_iterator.cpp',
     '../third_party/externals/dng_sdk/source/dng_tone_curve.cpp',
     '../third_party/externals/dng_sdk/source/dng_utils.cpp',
     '../third_party/externals/dng_sdk/source/dng_xy_coord.cpp',
     '../third_party/externals/dng_sdk/source/dng_jpeg_memory_source.cpp',
     '../third_party/externals/dng_sdk/source/dng_safe_arithmetic.cpp',
   ],
 }],
 }