[LyX/master] Fix configuring for Qt5 with autotools on non-Mac platforms.

[Enrico Forestieri]

commit ab3259885b989f8053d7af6112293c6a78a83170
Author: Enrico Forestieri <for...@lyx.org>
Date:   Thu Jan 1 18:44:01 2015 +0100

    Fix configuring for Qt5 with autotools on non-Mac platforms.

diff --git a/config/qt4.m4 b/config/qt4.m4
index aa94ae9..7852c8a 100644
--- a/config/qt4.m4
+++ b/config/qt4.m4
@@ -206,6 +206,7 @@ AC_DEFUN([QT_DO_PKG_CONFIG],
                if $lyx_use_winextras; then
                        qt_guilibs="$qt_guilibs Qt5WinExtras"
                fi
+               lyx_use_macextras=false
                PKG_CHECK_EXISTS(Qt5MacExtras, [lyx_use_macextras=true], [])
                if $lyx_use_macextras; then
                        qt_guilibs="$qt_guilibs Qt5MacExtras"