Fix compilation warnings/errors seen with newer versions of gcc compiler.

runtime/vm/dart_api_impl.cc

Index: runtime/vm/dart_api_impl.cc
===================================================================
--- runtime/vm/dart_api_impl.cc	(revision 265)
+++ runtime/vm/dart_api_impl.cc	(working copy)
@@ -35,7 +35,8 @@
 }
 
 
-DART_EXPORT Dart_Isolate Dart_CreateIsolate(void* snapshot, void* data) {
+DART_EXPORT Dart_Isolate Dart_CreateIsolate(const Dart_Snapshot* snapshot,
+                                            void* data) {
   ASSERT(Isolate::Current() == NULL);
   Isolate* isolate = Dart::CreateIsolate(snapshot, data);
   START_TIMER(time_total_runtime);
@@ -1481,7 +1482,8 @@
 }
 
 
-DART_EXPORT Dart_Result Dart_PostIntArray(Dart_Port port, intptr_t field_count,
+DART_EXPORT Dart_Result Dart_PostIntArray(Dart_Port port,
+                                          int field_count,
                                           intptr_t* data) {
   uint8_t* buffer = NULL;
   MessageWriter writer(&buffer, &allocator);