Add option to specify compiler executable.

Change-Id: I973da5e74be5a62461caacbc708288fb95e1b99b
diff --git a/runtime/runtime.h b/runtime/runtime.h
index f7074f6..261429e 100644
--- a/runtime/runtime.h
+++ b/runtime/runtime.h
@@ -104,6 +104,8 @@
     return is_explicit_gc_disabled_;
   }
 
+  std::string GetCompilerExecutable() const;
+
   const std::vector<std::string>& GetCompilerOptions() const {
     return compiler_options_;
   }
@@ -482,6 +484,7 @@
   bool is_concurrent_gc_enabled_;
   bool is_explicit_gc_disabled_;
 
+  std::string compiler_executable_;
   std::vector<std::string> compiler_options_;
   std::vector<std::string> image_compiler_options_;