Bump project requirement to C++17

src/base/bittorrent/common.h

@@ -30,5 +30,4 @@
 
 #include <QString>
 
-// TODO: Make it inline in C++17
-extern const QString QB_EXT;
+inline const QString QB_EXT {QStringLiteral(".!qB")};

src/base/bittorrent/ltunderlyingtype.h

@@ -30,9 +30,6 @@
 
 #include <type_traits>
 
-template <typename ...>
-using void_t = void;  // replace this with std::void_t in C++17
-
 template <typename T, typename = void>
 struct HasUnderlyingType
     : std::false_type
@@ -40,7 +37,7 @@ struct HasUnderlyingType
 };
 
 template <typename T>
-struct HasUnderlyingType<T, void_t<typename T::underlying_type>>
+struct HasUnderlyingType<T, std::void_t<typename T::underlying_type>>
     : std::true_type
 {
 };

src/base/bittorrent/session.cpp

@@ -291,9 +291,8 @@ namespace
     LowerLimited<T> lowerLimited(T limit, T ret) { return LowerLimited<T>(limit, ret); }
 
     template <typename T>
-    std::function<T (const T&)> clampValue(const T lower, const T upper)
+    auto clampValue(const T lower, const T upper)
     {
-        // TODO: change return type to `auto` when using C++17
         return [lower, upper](const T value) -> T
         {
             if (value < lower)

src/base/bittorrent/torrenthandleimpl.cpp

@@ -69,8 +69,6 @@
 #include "session.h"
 #include "trackerentry.h"
 
-const QString QB_EXT {QStringLiteral(".!qB")};
-
 using namespace BitTorrent;
 
 namespace