Fix build of archivers/ark on 10.3 (old clang). Make the return

type of the lambda explicit, to avoid this build error:

error: return type 'QString' must match previous return type 'const QString' when lambda expression has unspecified explicit return type
                return QString();

Reported by:	pkg-fallout
Approved by:	tcberner (mentor, implicit)

archivers/ark/files/patch-kerfuffle_pluginmanager.cpp

@@ -0,0 +1,11 @@
+--- kerfuffle/pluginmanager.cpp.orig	2018-03-03 22:55:29 UTC
++++ kerfuffle/pluginmanager.cpp
+@@ -258,7 +258,7 @@ QStringList PluginManager::sortByComment
+ bool PluginManager::libarchiveHasLzo()
+ {
+     // Step 1: look for the libarchive plugin, which is built against libarchive.
+-    const QString pluginPath = []() {
++    const QString pluginPath = []() -> const QString {
+         foreach (const QString &path, QCoreApplication::libraryPaths()) {
+             const QString pluginPath = QStringLiteral("%1/kerfuffle/kerfuffle_libarchive.so").arg(path);
+             if (QFileInfo::exists(pluginPath)) {