cc: Enable select syntax for cppflags

Bug: 325444956
Test: m
Test: m [custom build target with select in cppflags]
Change-Id: I7d27096526ce5b37afe447f900613a6fbb639986
diff --git a/rust/bindgen.go b/rust/bindgen.go
index f1579cc..d412ea1 100644
--- a/rust/bindgen.go
+++ b/rust/bindgen.go
@@ -285,7 +285,7 @@
 	if isCpp {
 		cflags = append(cflags, "-x c++")
 		// Add any C++ only flags.
-		cflags = append(cflags, esc(b.ClangProperties.Cppflags)...)
+		cflags = append(cflags, esc(b.ClangProperties.Cppflags.GetOrDefault(ctx, nil))...)
 	} else {
 		cflags = append(cflags, "-x c")
 	}