girepository/build: Actually use our compiler to generate GLib typelibs and fix parser leaks
We are overriding the default g-ir-compiler for local usage, but this is not actually happen since that's computed while parsing introspection
So generate the compiler as first thing, then in case handle the introspection data.
Then, focus on leak fixes, in fact before of this branch:
> ninja -C _build-asan girepository/introspection/GLib-2.0.typelib
SUMMARY: AddressSanitizer: 3381072 byte(s) leaked in 71436 allocation(s)
> ninja -C _build-asan girepository/introspection/Gio-2.0.typelib
SUMMARY: AddressSanitizer: 11119800 byte(s) leaked in 234356 allocation(s).
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Now: 0
Now, this is a program where leaking is not too much a problem, but it's still better to have the memory issues properly handled.
PS: I've also similar branch for GNOME/gobject-introspection, but I'm unsure if we want to update the code there at this point...