MSan does not understand inline asm. This change preinitializes cpuid

src/atomicops_internals_x86_gcc.cc

 // Copyright 2010 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 59 matching lines @@
 };
 
 } }  // namespace v8::internal
 
 namespace {
 
 // Initialize the AtomicOps_Internalx86CPUFeatures struct.
 void AtomicOps_Internalx86CPUFeaturesInit() {
   using v8::internal::AtomicOps_Internalx86CPUFeatures;
 
-  uint32_t eax;
-  uint32_t ebx;
-  uint32_t ecx;
-  uint32_t edx;
+  uint32_t eax = 0;
+  uint32_t ebx = 0;
+  uint32_t ecx = 0;
+  uint32_t edx = 0;
 
   // Get vendor string (issue CPUID with eax = 0)
   cpuid(eax, ebx, ecx, edx, 0);
   char vendor[13];
   v8::internal::OS::MemCopy(vendor, &ebx, 4);
   v8::internal::OS::MemCopy(vendor + 4, &edx, 4);
   v8::internal::OS::MemCopy(vendor + 8, &ecx, 4);
   vendor[12] = 0;
 
   // get feature flags in ecx/edx, and family/model in eax
@@ skipping 32 matching lines @@
 
 
 // A global to get use initialized on startup via static initialization :/
 AtomicOpsx86Initializer g_initer;
 
 }  // namespace
 
 #endif  // if x86
 
 #endif  // ifdef V8_ATOMICOPS_INTERNALS_X86_GCC_H_