Add c++20 builder on Windows

evergreen/config.yml

@@ -88,6 +88,10 @@ functions:
               set_cmake_var compiler_vars CMAKE_CXX_COMPILER PATH $(./evergreen/abspath.sh "${cxx_compiler}")
           fi
 
+          if [ -n "${cxx_standard|}" ]; then
+              set_cmake_var realm_vars CMAKE_CXX_STANDARD STRING "${cxx_standard}"
+          fi
+
           if [[ -z "${disable_tests_against_baas|}" && -z "${no_tests|}" ]]; then
               scheme="http"
               set_cmake_var baas_vars REALM_ENABLE_AUTH_TESTS BOOL On
@@ -1869,6 +1873,21 @@ buildvariants:
   tasks:
   - name: compile_test
 
+- name: windows-64-cxx20
+  display_name: "Windows x86_64 (c++20)"
+  run_on: windows-vsCurrent-large
+  expansions:
+    cmake_bindir: "/cygdrive/c/Program Files/CMake/bin"
+    cmake_generator: "Visual Studio 16 2019"
+    extra_flags: "-A x64"
+    max_jobs: $(($(grep -c proc /proc/cpuinfo) / 2))
+    fetch_missing_dependencies: On
+    curl_base: "/cygdrive/c/curl"
+    python3: "/cygdrive/c/python/python37/python.exe"
+    cxx_standard: 20
+  tasks:
+  - name: compile_only
+
 - name: windows-64-encryption
   display_name: "Windows x86_64 (Encryption enabled)"
   run_on: windows-vsCurrent-large