Uses NDK as C crosscompiler and ADB to run code on the target device.
Uses both :linux and :android features (android is almost a linux).
It also reserves a folder android-libs/ for putting precompiled
libraries to link agains (for example zstd for core compression).
See doc/internals-notes/Android-build.txt for more details
Our contrib build graph was already expressed in contrib/Makefile,
so ASDF wasn't doing anything to determine an execution schedule.
The new make-contrib.lisp script can parse '.asd' files more-or-less as-is,
removing ASDF from the critical path. With blocklist=sb-simd, this change
decreased the time in parallelized make-target-contrib to under 5 seconds
for me (down from >10) when run on as many cores as there are contrib dirs.
All defsystems are treated as if containing ":serial t", and there are
two invented keywords to bind/assign special variables around compilation.
We still install '.asd' files in $SBCL_HOME/contrib, and build uiop and asdf
so there should be no observable difference to users.
