Do not glob headers in out/

Currently, it skips it for files in out/soong/. This was a valid
assumption since all intermediate artifacts in soong are placed under
out/soong, and soong modules cannot depend on make modules.

However, this might change in multitree, since the headers provided by
build orchestrator will be under out/api_surfaces (next CL in this stack). The good side effect
of this is that we do not retrigger a rebuild of soong/build.ninja if a
new API file (.h/.map.txt) is added to this directory (ctx.GlobWithDeps
adds the files to the deps of out/soong/build.ninja).

Test: TH
Change-Id: I3c3722390d04a50d793b1646df00cdf7acb12b49
diff --git a/cc/library.go b/cc/library.go
index 41a68e3..ac64f8a 100644
--- a/cc/library.go
+++ b/cc/library.go
@@ -956,7 +956,7 @@
 	for _, path := range paths {
 		dir := path.String()
 		// Skip if dir is for generated headers
-		if strings.HasPrefix(dir, android.PathForOutput(ctx).String()) {
+		if strings.HasPrefix(dir, ctx.Config().OutDir()) {
 			continue
 		}