depends: qt: Explicitly stop using Xlib/libX11

Previously, in 683b7d7a3f and
0e752637a2, we accidentally broke QT's
ability to pick up Xlib thru the config.gui.tests.xlib configuration
test, which also means that config.gui.libraries.xcb_xlib wasn't run.

This resulted in a QT build that was implicitly -no-xcb-lib and
-no-feature-xlib.

This is actually a desired behaviour, as it means less required shared
objects for our final bitcoin-qt binary. Specifically, it eliminated the
libX11-xcb.so.1 and libX11.so.6 requirements.

In this commit, we explicitly build without Xlib. We should continue to
track upstream ticket https://bugreports.qt.io/browse/QTBUG-61452 which
talks about adding a -no-xlib (non-hidden) flag instead of the
-no-feature-xlib (hidden) flag.

depends/packages/qt.mk

@@ -98,6 +98,8 @@ endif
 
 $(package)_config_opts_linux  = -qt-xkbcommon-x11
 $(package)_config_opts_linux += -qt-xcb
+$(package)_config_opts_linux += -no-xcb-xlib
+$(package)_config_opts_linux += -no-feature-xlib
 $(package)_config_opts_linux += -system-freetype
 $(package)_config_opts_linux += -no-feature-sessionmanager
 $(package)_config_opts_linux += -fontconfig