Mac runtime fixes.

This is enough to let us run test-art-host on the Mac. The tests
that don't start a runtime (and thus don't try to dlopen(3)
libjavacore.dylib) succeed. The others fail, but I'm not sure how
the Linux tests find libjavacore.so, so I'm not sure how to fix
things for Mac OS.

Change-Id: Idf489fc09f0a8f64fbb60dfcdbca9c3df2d4fdcb
diff --git a/src/runtime.cc b/src/runtime.cc
index 904d959..114c538 100644
--- a/src/runtime.cc
+++ b/src/runtime.cc
@@ -221,8 +221,7 @@
 }
 
 void LoadJniLibrary(JavaVMExt* vm, const char* name) {
-  // TODO: OS_SHARED_LIB_FORMAT_STR
-  std::string mapped_name(StringPrintf("lib%s.so", name));
+  std::string mapped_name(StringPrintf(OS_SHARED_LIB_FORMAT_STR, name));
   std::string reason;
   if (!vm->LoadNativeLibrary(mapped_name, NULL, reason)) {
     LOG(FATAL) << "LoadNativeLibrary failed for \"" << mapped_name << "\": "