SUMMARY
Craft blueprint qtbase fails to build on Linux when using the Qt Patch Collection due to inability to find features.xlib and libs.xcb_xlib.

STEPS TO REPRODUCE
1. Prepare the OS for Craft:
> sudo apt update
> sudo apt install python3 python3-pip python3-venv build-essential git wget libxcb-xinerama0-dev
> sudo apt-get build-dep qt5-default #on new distros qt5-default is not available anymore try qtbase5-dev instead
2. Create and start a new Craft environment on an x86_64 system that runs macOS:
> python3 -c "$(wget https://raw.githubusercontent.com/KDE/craft/master/setup/CraftBootstrap.py -O -)" --prefix ~/CraftRoot
> source ~/CraftRoot/craft/craftenv.sh
3. Configure Craft to use KDE's Qt Patch Collection
> craft --set version=kde/5.15 libs/qt5
4. Build qtbase
> craft libs/qt5/qtbase

OBSERVED RESULT
libxcb dependency fails to be found:
> ERROR: Feature 'xcb-xlib' was enabled, but the pre-condition 'features.xlib && libs.xcb_xlib' failed.
> 
> Check config.log for details.
> 
> # Before sourcing craftenv.sh, ensure PKG_CONFIG_PATH includes xcb.pc, gl.pc etc
> export PKG_CONFIG_PATH=/usr/lib64/pkgconfig:/usr/share/pkgconfig
> # Install build dependencies on builder:
> sudo yum-builddep qt5-qtbase && sudo yum install libxkbcommon-x11-devel
> sudo apt build-dep qt5-default
> 
> Action: compile for libs/qt5/qtbase:kde/5.15 FAILED

EXPECTED RESULT
AppImage builds with the patch collection.

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: Ubuntu 18.04 and KDE neon Testing Edition
Qt Version: 5.15.5 kde-patched

ADDITIONAL INFORMATION
1. This issue has no relation with #456452 apart from the fact that it only happens when using Craft with the patch collection.
2. Running `export PKG_CONFIG_PATH=/usr/lib64/pkgconfig:/usr/share/pkgconfig` from bashrc or manually beforehand makes no difference in either OS.