Seperate asflags and cflags

This fixes a bug which was a misunderstanding of soong properties:
Soong's cflags pertain only to C and C++ language, whereas bazel's copts
pertain to all three languages. This change ensures that asflags are
added as specifically asflags, and the 'copts' for the static library
macro pertains only to C and C++ languages.

This requires a somewhat hacky workaround for asflags, however: Since
assembly sources also need includepath-related flags, this duplicates
these flags between copts and asflags. To reduce verbosity of
bp2build-generated targets, this also ensures that asflags are omitted
in cases where there are no assembly sources.

Test: Mixed build droid CI
Change-Id: Ic0babed1f90d6dc82e5788638681ce5b995043f8
diff --git a/cc/object.go b/cc/object.go
index 9f2db2e..5ded0e9 100644
--- a/cc/object.go
+++ b/cc/object.go
@@ -123,6 +123,7 @@
 // For bp2build conversion.
 type bazelObjectAttributes struct {
 	Srcs    bazel.LabelListAttribute
+	Srcs_as bazel.LabelListAttribute
 	Hdrs    bazel.LabelListAttribute
 	Deps    bazel.LabelListAttribute
 	Copts   bazel.StringListAttribute
@@ -179,13 +180,19 @@
 	// and this isn't typically done for cc_object.
 	srcs := compilerAttrs.srcs
 	srcs.Append(compilerAttrs.cSrcs)
-	srcs.Append(compilerAttrs.asSrcs)
+
+	asFlags := compilerAttrs.asFlags
+	if compilerAttrs.asSrcs.IsEmpty() {
+		// Skip asflags for BUILD file simplicity if there are no assembly sources.
+		asFlags = bazel.MakeStringListAttribute(nil)
+	}
 
 	attrs := &bazelObjectAttributes{
 		Srcs:    srcs,
+		Srcs_as: compilerAttrs.asSrcs,
 		Deps:    deps,
 		Copts:   compilerAttrs.copts,
-		Asflags: compilerAttrs.asFlags,
+		Asflags: asFlags,
 	}
 
 	props := bazel.BazelTargetModuleProperties{