Ignore return value of function declared with 'warn_unused_result'

Summary:
Ignore return value of function declared with 'warn_unused_result'

Addresses the following build failure that we get on some of our internal build environments:
caffe2/torch/csrc/deploy/environment.h:60:5: error: ignoring return value of function declared with 'warn_unused_result' attribute [-Werror,-Wunused-result] system(rmCmd.c_str());

Differential Revision: D39181069

fbshipit-source-id: e9516178b645729874a7cc1b82720789a1aca0d1

multipy/runtime/environment.h

@@ -66,7 +66,7 @@ class Environment {
   }
   virtual ~Environment() {
     auto rmCmd = "rm -rf " + extraPythonLibrariesDir_;
-    system(rmCmd.c_str());
+    (void)system(rmCmd.c_str());
   }
   virtual void configureInterpreter(Interpreter* interp) = 0;
   virtual const std::vector<std::string>& getExtraPythonPaths() {