Add e.g. Target: { Android_arm: { ...} } support to LabelAttribute.

LabelListAttribute support was already added, but LabelAttribute support is needed for cc_import rules.

Test: Added unit test for version_script, which is the only supported LabelAttribute so far.

Change-Id: I4e86e7391586e0780623d06b794e7399f0ccd50e
diff --git a/cc/bp2build.go b/cc/bp2build.go
index 339a489..711410c 100644
--- a/cc/bp2build.go
+++ b/cc/bp2build.go
@@ -568,6 +568,10 @@
 
 			linkopts.SetOsValueForTarget(os.Name, getBp2BuildLinkerFlags(baseLinkerProps))
 
+			if baseLinkerProps.Version_script != nil {
+				versionScript.SetOsValueForTarget(os.Name, android.BazelLabelForModuleSrcSingle(ctx, *baseLinkerProps.Version_script))
+			}
+
 			sharedLibs := baseLinkerProps.Shared_libs
 			dynamicDeps.SetOsValueForTarget(os.Name, android.BazelLabelForModuleDeps(ctx, sharedLibs))
 		}
@@ -582,6 +586,10 @@
 
 				linkopts.SetOsArchValueForTarget(os.Name, arch.Name, getBp2BuildLinkerFlags(baseLinkerProps))
 
+				if baseLinkerProps.Version_script != nil {
+					versionScript.SetOsArchValueForTarget(os.Name, arch.Name, android.BazelLabelForModuleSrcSingle(ctx, *baseLinkerProps.Version_script))
+				}
+
 				sharedLibs := baseLinkerProps.Shared_libs
 				dynamicDeps.SetOsArchValueForTarget(os.Name, arch.Name, android.BazelLabelForModuleDeps(ctx, sharedLibs))
 			}