build: add clang-cl build option on Windows

common.gypi

@@ -152,8 +152,10 @@
             'cflags': [ '-fPIC' ],
             'ldflags': [ '-fPIC' ]
           }],
+          ['clang==1', {
+            'msbuild_toolset': 'ClangCL',
+          }],
         ],
-        'msbuild_toolset': 'ClangCL',
         'msvs_settings': {
           'VCCLCompilerTool': {
             'BasicRuntimeChecks': 3,        # /RTC1
@@ -241,8 +243,10 @@
             'cflags': [ '-fPIC', '-I<(android_ndk_path)/sources/android/cpufeatures' ],
             'ldflags': [ '-fPIC' ]
           }],
+          ['clang==1', {
+            'msbuild_toolset': 'ClangCL',
+          }],
         ],
-        'msbuild_toolset': 'ClangCL',
         'msvs_settings': {
           'VCCLCompilerTool': {
             'conditions': [

configure.py

@@ -866,6 +866,13 @@
     default=None,
     help=argparse.SUPPRESS)
 
+parser.add_argument('--clang-cl',
+    action='store',
+    dest='clang_cl',
+    default=None,
+    help='Configure for clang-cl on Windows. This flag sets the GYP "clang" ' +
+         'variable to 1 and "llvm_version" to the specified value.')
+
 (options, args) = parser.parse_known_args()
 
 # Expand ~ in the install prefix now, it gets written to multiple files.
@@ -1042,9 +1049,9 @@ def get_gas_version(cc):
 # quite prepared to go that far yet.
 def check_compiler(o):
   if sys.platform == 'win32':
-    o['variables']['clang'] = 1
-    # Visual Studio 2022 ships with this version.
-    o['variables']['llvm_version'] = '17.0'
+    if options.clang_cl:
+      o['variables']['clang'] = 1
+      o['variables']['llvm_version'] = options.clang_cl
     if not options.openssl_no_asm and options.dest_cpu in ('x86', 'x64'):
       nasm_version = get_nasm_version('nasm')
       o['variables']['nasm_version'] = nasm_version

vcbuild.bat

@@ -32,6 +32,7 @@ set ltcg=
 set target_env=
 set noprojgen=
 set projgen=
+set clang_cl=
 set nobuild=
 set sign=
 set nosnapshot=
@@ -87,6 +88,7 @@ if /i "%1"=="arm64"         set target_arch=arm64&goto arg-ok
 if /i "%1"=="vs2022"        set target_env=vs2022&goto arg-ok
 if /i "%1"=="noprojgen"     set noprojgen=1&goto arg-ok
 if /i "%1"=="projgen"       set projgen=1&goto arg-ok
+if /i "%1"=="clang-cl"      set clang_cl=1&goto arg-ok
 if /i "%1"=="nobuild"       set nobuild=1&goto arg-ok
 if /i "%1"=="nosign"        set "sign="&echo Note: vcbuild no longer signs by default. "nosign" is redundant.&goto arg-ok
 if /i "%1"=="sign"          set sign=1&goto arg-ok
@@ -190,6 +192,8 @@ if defined nosnapshot       set configure_flags=%configure_flags% --without-snap
 if defined nonpm            set configure_flags=%configure_flags% --without-npm
 if defined nocorepack       set configure_flags=%configure_flags% --without-corepack
 if defined ltcg             set configure_flags=%configure_flags% --with-ltcg
+:: If clang-cl build is requested, set it to 17.0, which is the version shipped with VS 2022.
+if defined clang_cl         set configure_flags=%configure_flags% --clang-cl=17.0
 if defined release_urlbase  set configure_flags=%configure_flags% --release-urlbase=%release_urlbase%
 if defined download_arg     set configure_flags=%configure_flags% %download_arg%
 if defined enable_vtune_arg set configure_flags=%configure_flags% --enable-vtune-profiling
@@ -750,7 +754,7 @@ set exit_code=1
 goto exit
 
 :help
-echo vcbuild.bat [debug/release] [msi] [doc] [test/test-all/test-addons/test-doc/test-js-native-api/test-node-api/test-internet/test-tick-processor/test-known-issues/test-node-inspect/test-check-deopts/test-npm/test-v8/test-v8-intl/test-v8-benchmarks/test-v8-all] [ignore-flaky] [static/dll] [noprojgen] [projgen] [small-icu/full-icu/without-intl] [nobuild] [nosnapshot] [nonpm] [nocorepack] [ltcg] [licensetf] [sign] [ia32/x86/x64/arm64] [vs2022] [download-all] [enable-vtune] [lint/lint-ci/lint-js/lint-md] [lint-md-build] [format-md] [package] [build-release] [upload] [no-NODE-OPTIONS] [link-module path-to-module] [debug-http2] [debug-nghttp2] [clean] [cctest] [no-cctest] [openssl-no-asm]
+echo vcbuild.bat [debug/release] [msi] [doc] [test/test-all/test-addons/test-doc/test-js-native-api/test-node-api/test-internet/test-tick-processor/test-known-issues/test-node-inspect/test-check-deopts/test-npm/test-v8/test-v8-intl/test-v8-benchmarks/test-v8-all] [ignore-flaky] [static/dll] [noprojgen] [projgen] [clang] [small-icu/full-icu/without-intl] [nobuild] [nosnapshot] [nonpm] [nocorepack] [ltcg] [licensetf] [sign] [ia32/x86/x64/arm64] [vs2022] [download-all] [enable-vtune] [lint/lint-ci/lint-js/lint-md] [lint-md-build] [format-md] [package] [build-release] [upload] [no-NODE-OPTIONS] [link-module path-to-module] [debug-http2] [debug-nghttp2] [clean] [cctest] [no-cctest] [openssl-no-asm]
 echo Examples:
 echo   vcbuild.bat                          : builds release build
 echo   vcbuild.bat debug                    : builds debug build