On Windows, use c++20 mode as correctly needed for designated initial…

…izers.

Designated initializers is technically only supported starting with c++20,
and the compiler on Windows points that out with an error.

.bazelrc

@@ -21,7 +21,8 @@ common:macos --features=-supports_dynamic_linker --linkopt=-framework --linkopt=
 # Force the use clang-cl on Windows instead of MSVC. MSVC has some issues with
 # the codebase, so we focus the effort for now is to have a Windows Verible
 # compiled with clang-cl before fixing the issues unique to MSVC.
-common:windows --compiler=clang-cl --cxxopt=/std:c++17 --host_cxxopt=/std:c++17 --client_env=BAZEL_CXXOPTS=/std:c++17
+# Since we use designated initializers (C99 ... but >= c++20), compiler really wants the c++20 mode
+common:windows --compiler=clang-cl --cxxopt=/std:c++20 --host_cxxopt=/std:c++20 --client_env=BAZEL_CXXOPTS=/std:c++20
 
 # Address sanitizer settings.
 build:asan --strip=never