Fix warning when building qmake with MSVC

Fix the C4715 warning for 'hostToTargetPathEnum' by marking the qFatal()
branch as unreachable.

Change-Id: Id065daaffd865e85985b1a8e0ac2eba4a2ff0b1c
Reviewed-by: Alexandru Croitor <alexandru.croitor@qt.io>

qmake/qmakelibraryinfo.cpp

@@ -145,6 +145,7 @@ static QLibraryInfo::LibraryPath hostToTargetPathEnum(int loc)
             return mapping[i].second;
     }
     qFatal("Unhandled host path %d in hostToTargetPathEnum.", loc);
+    Q_UNREACHABLE();
 }
 
 struct LocationInfo