[clang-cl] Set _MSVC_LANG to 202002L with /std:c++20

MSVC says this should be 202002L for /std:c++20, and of VS16.11
that's indeed the case (older versions warn that they don't
understand /std:c++20, and then cl.exe defaults to C++14 and
sets _MSVC_LANG to 201402 accordingly).

Differential Revision: https://reviews.llvm.org/D114867

GitOrigin-RevId: 3f643f166494826144bad05eaa3ae14508788df6
diff --git a/lib/Basic/Targets/OSTargets.cpp b/lib/Basic/Targets/OSTargets.cpp
index 4d9a462..abf46fc 100644
--- a/lib/Basic/Targets/OSTargets.cpp
+++ b/lib/Basic/Targets/OSTargets.cpp
@@ -182,7 +182,7 @@
 
     if (Opts.isCompatibleWithMSVC(LangOptions::MSVC2015)) {
       if (Opts.CPlusPlus20)
-        Builder.defineMacro("_MSVC_LANG", "201705L");
+        Builder.defineMacro("_MSVC_LANG", "202002L");
       else if (Opts.CPlusPlus17)
         Builder.defineMacro("_MSVC_LANG", "201703L");
       else if (Opts.CPlusPlus14)
diff --git a/test/Preprocessor/predefined-win-macros.c b/test/Preprocessor/predefined-win-macros.c
index 928ca6f..2ded133 100644
--- a/test/Preprocessor/predefined-win-macros.c
+++ b/test/Preprocessor/predefined-win-macros.c
@@ -45,9 +45,9 @@
 // CHECK-MS-NOT: GXX
 
 // RUN: %clang_cc1 %s -x c++ -E -dM -triple i686-pc-win32 -fms-extensions -fms-compatibility \
-// RUN:     -fms-compatibility-version=19.00 -std=c++2a -o - | FileCheck -match-full-lines %s --check-prefix=CHECK-MS-CPP2A
+// RUN:     -fms-compatibility-version=19.00 -std=c++20 -o - | FileCheck -match-full-lines %s --check-prefix=CHECK-MS-CPP2A
 // CHECK-MS-CPP2A: #define _MSC_VER 1900
-// CHECK-MS-CPP2A: #define _MSVC_LANG 201705L
+// CHECK-MS-CPP2A: #define _MSVC_LANG 202002L
 
 // RUN: %clang_cc1 -triple i386-windows %s -E -dM -o - \
 // RUN:   | FileCheck -match-full-lines %s --check-prefix=CHECK-X86-WIN