Handle arch-specific/not properties the same.

Refactor arch-handling code to return a "no-config" axis which allows
handling non-arch configed properties the same way as arch-configed
properties.

Test: build/bazel/ci/bp2build.sh
Change-Id: I485b35fd91c28501fe2055234dc9b278488bf4b5
diff --git a/android/arch.go b/android/arch.go
index 7ca7336..f7eb963 100644
--- a/android/arch.go
+++ b/android/arch.go
@@ -1967,6 +1967,7 @@
 		srcType := reflect.ValueOf(generalProp).Type()
 		if srcType == dstType {
 			archProperties = m.archProperties[i]
+			axisToProps[bazel.NoConfigAxis] = ArchVariantProperties{"": generalProp}
 			break
 		}
 	}