Mixed builds: propagate includes from cc_* targets

This allows us to remove libasync_safe from the mixed builds denylist.

Test: mixed_libc.sh CI script
Change-Id: Ibafd231284864078bf30340f919d39e5098843ce
diff --git a/cc/linkable.go b/cc/linkable.go
index 8fe0b4a..2351fc3 100644
--- a/cc/linkable.go
+++ b/cc/linkable.go
@@ -283,7 +283,7 @@
 	systemIncludes := android.PathsForBazelOut(ctx, ccInfo.SystemIncludes)
 
 	return FlagExporterInfo{
-		IncludeDirs:       includes,
-		SystemIncludeDirs: systemIncludes,
+		IncludeDirs:       android.FirstUniquePaths(includes),
+		SystemIncludeDirs: android.FirstUniquePaths(systemIncludes),
 	}
 }