VM/Mac: Prevent dead_strip from removing API functions.

runtime/include/dart_api.h

 /*
  * Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
  * for details. All rights reserved. Use of this source code is governed by a
  * BSD-style license that can be found in the LICENSE file.
  */
 
 #ifndef INCLUDE_DART_API_H_
 #define INCLUDE_DART_API_H_
 
 /** \mainpage Dart Embedding API Reference
@@ skipping 36 matching lines @@
 #else
 /* __STDC_FORMAT_MACROS has to be defined before including <inttypes.h> to
  * enable platform independent printf format specifiers. */
 #ifndef __STDC_FORMAT_MACROS
 #define __STDC_FORMAT_MACROS
 #endif
 #include <inttypes.h>
 #include <stdbool.h>
 #if __GNUC__ >= 4
 #if defined(DART_SHARED_LIB)
-#define DART_EXPORT DART_EXTERN_C __attribute__ ((visibility("default")))
+#define DART_EXPORT DART_EXTERN_C __attribute__ ((visibility("default"))) \
+    __attribute((used))
 #else
 #define DART_EXPORT DART_EXTERN_C
 #endif
 #else
 #error Tool chain not supported.
 #endif
 #endif
 
 #include <assert.h>
 
@@ skipping 2893 matching lines @@
     intptr_t* vm_isolate_snapshot_size,
     uint8_t** isolate_snapshot_buffer,
     intptr_t* isolate_snapshot_size,
     uint8_t** instructions_snapshot_buffer,
     intptr_t* instructions_snapshot_size);
 
 
 DART_EXPORT bool Dart_IsRunningPrecompiledCode();
 
 #endif  /* INCLUDE_DART_API_H_ */  /* NOLINT */