Add cpp20 to validatekeymaps

We need this to take advantage of default-generated comparison
operators.

Bug: 278299254
Test: m
Change-Id: I4b0bd848606936378f16e95d767afd68b25ab4d8
diff --git a/tools/validatekeymaps/Android.bp b/tools/validatekeymaps/Android.bp
index 25373f9..554f64e 100644
--- a/tools/validatekeymaps/Android.bp
+++ b/tools/validatekeymaps/Android.bp
@@ -15,7 +15,7 @@
 
 cc_binary_host {
     name: "validatekeymaps",
-
+    cpp_std: "c++20",
     srcs: ["Main.cpp"],
 
     cflags: [