Allow importing starlark code in makefiles

Adds a new `$(call run-starlark,my/starlark/file.bzl)` function that
will run the starlark file and set all the variables in the
variables_to_export_to_make dictionary as make variables.

Fixes: 280685526
Test: m nothing repeatedly causes no ninja regeneration, but touching all_versions.bzl does. go test, ./out/rbcrun -mode=rbc ./build/make/tests/run.rbc
Change-Id: Ic72e18dd28dba8233ba2dfb658b5d03ccece1bfd