Fix lto build on clang by marking HolderBase::operator() as abstract (#12)

DarkDimius · arun11299 · commit 4cc467e2aab2 · 2018-03-07T09:47:12.000+05:30
diff --git a/subprocess.hpp b/subprocess.hpp
@@ -611,7 +611,7 @@ class preexec_func
 
 private:
   struct HolderBase {
-    virtual void operator()() const;
+    virtual void operator()() const = 0;
   };
   template <typename T>
   struct FuncHolder: HolderBase {
