I try to read and understand how wrap-qt-program in qt-utils.scm works.
When building QT program, Guix builder populates qt related environment
variable, and wrap-qt-program just record it into wrapper.

However, the wrap behaviour in qt-build-system is quite different, it
search all inputs and mark them should be included in envvar definition
if correspond directory exists.

Another difference is, wrap-qt-program will include the directory of
output in envvar but qt-build-system won't do.

I'm not sure whether we need to include output, and don't know recording
build time environment follows reproducible build rule or not. Maybe we
need an expert on Qt programming/packaging to give us some hints? :(

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Zihao