[native_toolchain_c] Support Clang on Windows 2

pkgs/native_toolchain_c/lib/src/cbuilder/compiler_resolver.dart

@@ -218,7 +218,11 @@ class CompilerResolver {
     }
 
     final compilerTool = compiler.tool;
-    assert(compilerTool == cl);
+    if (compilerTool != cl) {
+      // If Clang is used on Windows, and we could discover the MSVC
+      // installation, then Clang should be able to discover it as well.
+      return {};
+    }
     final vcvarsScript =
         (await vcvars(compiler).defaultResolver!.resolve(logger: logger)).first;
     return await environmentFromBatchFile(

pkgs/native_toolchain_c/lib/src/cbuilder/run_cbuilder.dart

@@ -131,6 +131,9 @@ class RunCBuilder {
   }
 
   Future<void> runClangLike({required ToolInstance tool}) async {
+    // Clang for Windows requires the MSVC Developer Environment.
+    final environment = await _resolver.resolveEnvironment(tool);
+
     final isStaticLib = staticLibrary != null;
     Uri? archiver_;
     if (isStaticLib) {
@@ -176,6 +179,7 @@ class RunCBuilder {
           targetMacOSVersion,
           [sourceFiles[i]],
           objectFile,
+          environment,
         );
         objectFiles.add(objectFile);
       }
@@ -189,6 +193,7 @@ class RunCBuilder {
         logger: logger,
         captureOutput: false,
         throwOnUnexpectedExitCode: true,
+        environment: environment,
       );
     } else {
       await _compile(
@@ -200,6 +205,7 @@ class RunCBuilder {
         targetMacOSVersion,
         sourceFiles,
         dynamicLibrary != null ? outDir.resolveUri(dynamicLibrary!) : null,
+        environment,
       );
     }
   }
@@ -214,9 +220,11 @@ class RunCBuilder {
     int? targetMacOSVersion,
     Iterable<String> sourceFiles,
     Uri? outFile,
+    Map<String, String> environment,
   ) async {
     await runProcess(
       executable: toolInstance.uri,
+      environment: environment,
       arguments: [
         if (codeConfig.targetOS == OS.android) ...[
           '--target='