Protect local static object construction in ARMCC

Implement the functions __cxa_guard_acquire, __cxa_guard_release
and __cxa_guard_abort for ARMCC so local static object construction is
thread safe.

Author: c1728p9

platform/mbed_retarget.cpp

@@ -977,6 +977,10 @@ extern "C" void __env_unlock( struct _reent *_r )
     __rtos_env_unlock(_r);
 }
 
+#endif
+
+#if defined (__GNUC__) || defined(__CC_ARM) || (defined (__ARMCC_VERSION) && (__ARMCC_VERSION >= 6010050))
+
 #define CXA_GUARD_INIT_DONE             (1 << 0)
 #define CXA_GUARD_INIT_IN_PROGRESS      (1 << 1)
 #define CXA_GUARD_MASK                  (CXA_GUARD_INIT_DONE | CXA_GUARD_INIT_IN_PROGRESS)