bazel: switch to C++20

.bazelrc

@@ -5,8 +5,8 @@ build --enable_runfiles
 build --incompatible_strict_action_env
 
 # required for googletest
-build:linux --cxxopt=-std=c++17
-build:macos --cxxopt=-std=c++17
+build:linux --cxxopt=-std=c++20
+build:macos --cxxopt=-std=c++20
 
 common:ci --announce_rc
 common:ci --verbose_failures

bazel/copts.bzl

@@ -2,11 +2,11 @@ load("@bazel_skylib//lib:selects.bzl", "selects")
 
 COPTS = selects.with_or({
     ("//conditions:default", "@rules_cc//cc/compiler:clang", "@rules_cc//cc/compiler:gcc", "@rules_cc//cc/compiler:mingw-gcc"): [
-        "-std=c++17",
+        "-std=c++20",
         "-w",
     ],
     ("@rules_cc//cc/compiler:msvc-cl", "@rules_cc//cc/compiler:clang-cl"): [
-        "/std:c++17",
+        "/std:c++20",
         "/permissive-",
         "/w",
     ],