bp2build: Add special arch-variant targets.

Soong supports additional arch-variant targets based on arch/os aside
from strictly arch/os names. Handle the unconverted cases based solely
on arch/os.

Test: build/bazel/ci/bp2build.sh
Change-Id: I8dc987b1aa4a4ea646dd5b03a94b84297ba6113a
diff --git a/bp2build/testing.go b/bp2build/testing.go
index 6c322ee..7c2f43a 100644
--- a/bp2build/testing.go
+++ b/bp2build/testing.go
@@ -283,7 +283,7 @@
 			return
 		}
 
-		paths := bazel.MakeLabelListAttribute(android.BazelLabelForModuleSrcExcludes(ctx, m.props.Arch_paths, m.props.Arch_paths_exclude))
+		paths := bazel.LabelListAttribute{}
 
 		for axis, configToProps := range m.GetArchVariantProperties(ctx, &customProps{}) {
 			for config, props := range configToProps {