Use C++20 for MSVC builds as well

Build only ANGLE libraries on MSVC,
as there are many failures in tests,
which are beyond our scope to fix.

Bug: chromium:1380553
Change-Id: I7142730bfa1fc847630ff8115709e435aecf487a
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/4286569
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Auto-Submit: Yuly Novikov <ynovikov@chromium.org>
Commit-Queue: Geoff Lang <geofflang@chromium.org>

BUILD.gn

@@ -39,8 +39,10 @@ declare_args() {
 
   # Don't build extra (test, samples etc) for Windows UWP. We don't have
   # infrastructure (e.g. windowing helper functions) in place to run them.
+  # Also don't build them with MSVC, because tests and unused dependencies
+  # often have problems building with it, e.g. for C++20.
   angle_build_all = !build_with_chromium && !angle_is_winuwp &&
-                    angle_has_build && angle_build_tests
+                    !angle_is_msvc && angle_has_build && angle_build_tests
 
   # Enable generating current commit information using git
   angle_enable_commit_id = true

build_overrides/build.gni

@@ -33,9 +33,6 @@ enable_java_templates = true
 # Build with fewer Android dependencies
 limit_android_deps = true
 
-# Use C++17 instead of C++20 in MSVC builds
-msvc_use_cxx17 = true
-
 # Standalone ANGLE is used in places that are extremely performance sensitive,
 # such as the system graphics driver on Android. ANGLE validates arguments at
 # the API boundary and assumes that all bounds, et cetera are valid elsewhere

gni/angle.gni

@@ -135,6 +135,7 @@ declare_args() {
 
   # There's no "is_winuwp" helper in BUILDCONFIG.gn, so we define one ourselves
   angle_is_winuwp = is_win && target_os == "winuwp"
+  angle_is_msvc = is_win && !is_clang
 
   # Default to using "_angle" suffix on Android
   if (is_android) {