contribs: Add Qt11Extras

This is required when building for linux, and might cause a system
provided version to be used, causing conflicts during linking.

Typically, the error message at link time will look like this:

    /usr/bin/ld: .libs/libqt_plugin.so: version node not found for symbol qt_version_tag@Qt_5.10

Co-authored-by: Alexandre Janniaux <ajanni@videolabs.io>

contrib/src/qtx11extras/SHA512SUMS

+59155fc97da3f7571da37dd63bed79f61580fa4df7d4886df51520ea6fe8e01e7c09f0aa9caaeaa986c0e5eac11d4479c99c892da4d075c6369b535fd505b084  qtx11extras-5.15.1.tar.xz

contrib/src/qtx11extras/rules.mak

+# qtx11extras
+
+QTX11_VERSION_MAJOR := 5.15
+QTX11_VERSION:= $(QTX11_VERSION_MAJOR).1
+QTX11_URL := http://download.qt.io/official_releases/qt/$(QTX11_VERSION_MAJOR)/$(QTX11_VERSION)/submodules/qtx11extras-everywhere-src-$(QTX11_VERSION).tar.xz
+
+DEPS_qtx11extras += qt $(DEPS_qt)
+
+$(TARBALLS)/qtx11extras-$(QTX11_VERSION).tar.xz:
+	$(call download,$(QTX11_URL))
+
+.sum-qtx11extras: qtx11extras-$(QTX11_VERSION).tar.xz
+
+qtx11extras: qtx11extras-$(QTX11_VERSION).tar.xz .sum-qtx11extras
+	$(UNPACK)
+	mv qtx11extras-everywhere-src-$(QTX11_VERSION) qtx11extras-$(QTX11_VERSION)
+	$(MOVE)
+
+.qtx11extras: qtx11extras
+	cd $< && $(PREFIX)/lib/qt5/bin/qmake
+	# Make && Install libraries
+	cd $< && $(MAKE) install INSTALL_FILE="$(QT_QINSTALL)" VLC_PREFIX="$(PREFIX)"
+	touch $@