bp2build: add configurable attribute (select) support.
This CL adds a basic framework to support configurable string_list
attributes, selecting on the Arch variant (x86, x86_64, arm, arm64).
It offers fine-grained controls to map individual configurable
properties (arch_variant) to configurable Bazel attributes, starting
with the string_list type for the copts property for cc_object.
This design is primarily motivated to have minimal boilerplate in
bp2build mutators, allowing anyone to opt-in configurable attributes,
and modify intermediate states before passing them on into the
CreateBazelTargetModule instantiator.
Fixes: 178130668
Test: go tests
Test: build/bazel/scripts/milestone-2/demo.sh
Change-Id: Id6f04d7c560312a93e193d7ca4e1b7ceb6062260
diff --git a/bp2build/Android.bp b/bp2build/Android.bp
index 7d748ec..8deb5a2 100644
--- a/bp2build/Android.bp
+++ b/bp2build/Android.bp
@@ -10,6 +10,7 @@
"bp2build.go",
"build_conversion.go",
"bzl_conversion.go",
+ "configurability.go",
"conversion.go",
"metrics.go",
],