file_util: Make move constructor/assignment operator and related functions noexcept

Without this, it's possible to get compilation failures in the (rare) scenario where
a container is used to store a bunch of live IOFile instances, as they may be using
std::move_if_noexcept under the hood. Given these definitely don't throw exceptions
this is also not incorrect to add either.

src/common/file_util.h

@@ -160,10 +160,10 @@ public:
 
     ~IOFile();
 
-    IOFile(IOFile&& other);
-    IOFile& operator=(IOFile&& other);
+    IOFile(IOFile&& other) noexcept;
+    IOFile& operator=(IOFile&& other) noexcept;
 
-    void Swap(IOFile& other);
+    void Swap(IOFile& other) noexcept;
 
     bool Open(const std::string& filename, const char openmode[]);
     bool Close();