reproc++: Make deleter a static function.

No reason for a lambda when a static function will do.

reproc++/src/reproc.cpp

@@ -62,9 +62,9 @@ static reproc_options reproc_options_from(const options &options, bool fork)
   };
 }
 
-const auto deleter = [](reproc_t *process) noexcept {
+static void deleter(reproc_t *process) noexcept {
   reproc_destroy(process);
-};
+}
 
 process::process() : impl_(reproc_new(), deleter) {}
 process::~process() noexcept = default;