This adds add-build-extensions which is similar to add-extensions
except the extension is added at build-init time, so can be
used during the build. It can also optionally be removed after
the build is done.
This depends on the flatpak work in:
https://github.com/flatpak/flatpak/pull/1598
With this I was able to build the following app which runs 32bit binaries
in a 64bit build:
```
{
"app-id": "org.example.Multilib",
"runtime": "org.freedesktop.Platform",
"sdk": "org.freedesktop.Sdk",
"runtime-version": "1.6",
"command": "/usr/bin/true",
"add-build-extensions": {
"org.freedesktop.Platform.Compat32": {
"directory": "lib/32bit",
"add-ld-path": "lib",
"version": "1.6"
}
},
"modules": [
{
"name": "test 32bit",
"buildsystem": "simple",
"build-commands": [
"ln -s /app/lib/32bit/lib/ld-linux.so.2 /app/lib/ld-linux.so.2",
"/app/lib/32bit/bin/echo echoing from 32bit world"
]
}
]
}
```
Closes: #129
Approved by: alexlarsson
Alexander Larsson