fix issue google#1521

use default constructor of pthread_t in order to initialize mutex

googletest/include/gtest/internal/gtest-port.h

@@ -2093,13 +2093,8 @@ class MutexBase {
      extern ::testing::internal::MutexBase mutex
 
 // Defines and statically (i.e. at link time) initializes a static mutex.
-// The initialization list here does not explicitly initialize each field,
-// instead relying on default initialization for the unspecified fields. In
-// particular, the owner_ field (a pthread_t) is not explicitly initialized.
-// This allows initialization to work whether pthread_t is a scalar or struct.
-// The flag -Wmissing-field-initializers must not be specified for this to work.
 #  define GTEST_DEFINE_STATIC_MUTEX_(mutex) \
-     ::testing::internal::MutexBase mutex = { PTHREAD_MUTEX_INITIALIZER, false }
+     ::testing::internal::MutexBase mutex = { PTHREAD_MUTEX_INITIALIZER, false, pthread_t() }
 
 // The Mutex class can only be used for mutexes created at runtime. It
 // shares its API with MutexBase otherwise.