note: some files have two versions in them, e.g.:
```
assert CffiRecipe._version == "1.15.1"
class CffiRecipePinned(util.InheritedRecipeMixin, CffiRecipe):
version = "1.17.1"
```
The assert is left there as I think it might be useful to get a failure if we rebase p4a
and the upstream recipe version changes. There might be substantial changes in the upstream
recipe that we need to adapt to. In the happy case, if we rebase p4a, we just have to manually
update these asserts to the new versions at that time.
The current system python in the docker baseimage is py3.9, while the
targetpython and hostpython built by p4a are py3.8, and this was causing
linker issues in the pyqt5 build.
It is also cleaner IMHO to have p4a handle what is needed for a recipe
instead of assuming it is available in the system. (and I think this is
how other existing recipes work)
fixes https://github.com/spesmilo/electrum/issues/8016
