Merge "Bump the default from gnu++17 to gnu++20." into main

cc/cc_test.go

@@ -4818,7 +4818,7 @@ func TestIncludeDirectoryOrdering(t *testing.T) {
 
 	cflags := []string{"-Werror", "-std=candcpp"}
 	cstd := []string{"-std=gnu17", "-std=conly"}
-	cppstd := []string{"-std=gnu++17", "-std=cpp", "-fno-rtti"}
+	cppstd := []string{"-std=gnu++20", "-std=cpp", "-fno-rtti"}
 
 	lastIncludes := []string{
 		"out/soong/ndk/sysroot/usr/include",

cc/config/global.go

@@ -357,7 +357,7 @@ var (
 	}
 
 	CStdVersion               = "gnu17"
-	CppStdVersion             = "gnu++17"
+	CppStdVersion             = "gnu++20"
 	ExperimentalCStdVersion   = "gnu2x"
 	ExperimentalCppStdVersion = "gnu++2a"