diff --git a/cc/makevars.go b/cc/makevars.go
index f7f8b60..2d71db6 100644
--- a/cc/makevars.go
+++ b/cc/makevars.go
@@ -279,6 +279,10 @@
 		// This is used by external/gentoo/...
 		ctx.Strict("CLANG_CONFIG_"+target.Arch.ArchType.Name+"_"+typePrefix+"TRIPLE",
 			toolchain.ClangTriple())
+
+		ctx.Strict(makePrefix+"CLANG_SUPPORTED", "true")
+	} else {
+		ctx.Strict(makePrefix+"CLANG_SUPPORTED", "")
 	}
 
 	ctx.Strict(makePrefix+"CC", gccCmd(toolchain, "gcc"))