sandbox_linux: set CCACHE_DIR as a writable path

fixes Read-only dir issue when using ccache

Signed-off-by: daniml3 <danimoral1001@gmail.com>
Change-Id: I99afe644c8ee0e0b881c1643fef0cb31b83bcd17
diff --git a/ui/build/sandbox_linux.go b/ui/build/sandbox_linux.go
index edb3b66..386dc55 100644
--- a/ui/build/sandbox_linux.go
+++ b/ui/build/sandbox_linux.go
@@ -228,6 +228,10 @@
 		sandboxArgs = append(sandboxArgs, "-N")
 	}
 
+	if ccacheDir := os.Getenv("CCACHE_DIR"); ccacheDir != "" {
+		sandboxArgs = append(sandboxArgs, "-B", ccacheDir)
+	}
+
 	// Stop nsjail from parsing arguments
 	sandboxArgs = append(sandboxArgs, "--")