Use lazy instance initializer to remove static initializers in two places.

src/platform-posix.cc

Index: src/platform-posix.cc
===================================================================
--- src/platform-posix.cc	(revision 11012)
+++ src/platform-posix.cc	(working copy)
@@ -127,13 +127,13 @@
 }
 
 
-static Mutex* math_function_mutex = OS::CreateMutex();
+static LazyMutex math_function_mutex = LAZY_MUTEX_INITIALIZER;
 
 #define UNARY_MATH_FUNCTION(name, generator)             \
 static UnaryMathFunction fast_##name##_function = NULL;  \
 double fast_##name(double x) {                           \
   if (fast_##name##_function == NULL) {                  \
-    ScopedLock lock(math_function_mutex);                \
+    ScopedLock lock(math_function_mutex.Pointer());      \
     UnaryMathFunction temp = generator;                  \
     MemoryBarrier();                                     \
     fast_##name##_function = temp;                       \