chore: sync with ecsact_common (#120)

Author: seaubot

bazel/BUILD.bazel

@@ -0,0 +1,4 @@
+config_setting(
+    name = "compiler_emscripten",
+    flag_values = {"@bazel_tools//tools/cpp:compiler": "emscripten"},
+)

bazel/copts.bzl

@@ -1,7 +1,10 @@
 load("@bazel_skylib//lib:selects.bzl", "selects")
 
-# Ecsact repositories currently only support clang and cl
+# Ecsact repositories currently only support clang, cl, and emscripten
 copts = selects.with_or({
+    (Label("//bazel:compiler_emscripten")): [
+        "-std=c++20",
+    ],
     ("@rules_cc//cc/compiler:clang"): [
         "-std=c++2b",
         "-fexperimental-library",