Fix possible ToolTask hang (#10297)

Using different overload of WaitForExit to avoid situation when grandchild process is keeping the MSBuild waiting

documentation/wiki/ChangeWaves.md

@@ -28,6 +28,7 @@ A wave of features is set to "rotate out" (i.e. become standard functionality) t
 - [Convert.ToString during a property evaluation uses the InvariantCulture for all types](https://github.com/dotnet/msbuild/pull/9874)
 - [Fix oversharing of build results in ResultsCache](https://github.com/dotnet/msbuild/pull/9987)
 - [Add ParameterName and PropertyName to TaskParameterEventArgs](https://github.com/dotnet/msbuild/pull/10130)
+- [The ToolTask only waits for its child process to end before returning, instead of waiting for grandchildren](https://github.com/dotnet/msbuild/pull/10297)
 
 ### 17.10
 - [AppDomain configuration is serialized without using BinFmt](https://github.com/dotnet/msbuild/pull/9320) - feature can be opted out only if [BinaryFormatter](https://learn.microsoft.com/en-us/dotnet/api/system.runtime.serialization.formatters.binary.binaryformatter) is allowed at runtime by editing `MSBuild.runtimeconfig.json`

src/Utilities/ToolTask.cs

@@ -1053,7 +1053,16 @@ private void TerminateToolProcess(Process proc, bool isBeingCancelled)
         /// <param name="proc"></param>
         private static void WaitForProcessExit(Process proc)
         {
-            proc.WaitForExit();
+            if (ChangeWaves.AreFeaturesEnabled(ChangeWaves.Wave17_12))
+            {
+                // Using overload with timeout prevents hanging in case that grandchild process is still running
+                // See https://github.com/dotnet/runtime/issues/51277 and https://github.com/dotnet/msbuild/issues/2981#issuecomment-818581362
+                proc.WaitForExit(int.MaxValue);
+            }
+            else
+            {
+                proc.WaitForExit();
+            }
 
             // Process.WaitForExit() may return prematurely. We need to check to be sure.
             while (!proc.HasExited)