Disable assembly optimizations in MemorySanitizer builds of libjpeg_turbo.

libjpeg.gyp

Index: libjpeg.gyp
===================================================================
--- libjpeg.gyp	(revision 251746)
+++ libjpeg.gyp	(working copy)
@@ -136,7 +136,7 @@
             'simd/jsimdcpu.asm',
           ],
         }],
-        [ 'target_arch=="x64"', {
+        [ 'target_arch=="x64" and msan!=1', {
           'sources': [
             'simd/jsimd_x86_64.c',
             'simd/jccolss2-64.asm',
@@ -156,6 +156,13 @@
             'simd/jiss2red-64.asm',
           ],
         }],
+        # MemorySanitizer doesn't support assembly code, so keep it disabled in
+        # MSan builds for now.
+        [ 'msan==1', {
+          'sources': [
+            'jsimd_none.c',
+          ],
+        }],
         # The ARM SIMD implementation can be used for devices that support
         # the NEON instruction set. This can safely be done dynamically by
         # probing CPU features at runtime, if you wish.