These build errors are caused because eglplatform.h is included before Qt
headers and it pulls X11 headers which contain many problematic macros.
Apparently X11 headers aren't required here anyways so let's just disable
them from being pulled in.
* Use an older glibc so resulting binaries can run
on older systems (without having to link statically
against glibc)
* Call packages static-compat-* to make it clear that
these packages are intended for compatibility with
older distributions
* Add further libraries to get static-compat-qt6-base
and some other static-compat-qt6-* packages building
* Add certain variables to find Qt's dependencies to the CMake
toolchain file because these variables would otherwise needed to
be set every time Qt 6 is used
* Add a static variant
* Not fully tested yet
* Further repos besides base and svg will be added later
