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/bazel/properties.go b/bazel/properties.go
index 0dd47da..7ecc92b 100644
--- a/bazel/properties.go
+++ b/bazel/properties.go
@@ -558,6 +558,19 @@
 	return len(lla.ConfigurableValues) > 0
 }
 
+// IsEmpty returns true if the attribute has no values under any configuration.
+func (lla LabelListAttribute) IsEmpty() bool {
+	if len(lla.Value.Includes) > 0 {
+		return false
+	}
+	for axis, _ := range lla.ConfigurableValues {
+		if lla.ConfigurableValues[axis].HasConfigurableValues() {
+			return false
+		}
+	}
+	return true
+}
+
 // ResolveExcludes handles excludes across the various axes, ensuring that items are removed from
 // the base value and included in default values as appropriate.
 func (lla *LabelListAttribute) ResolveExcludes() {