Make attachdebugger flag work on non-Windows (#79499)

These compiler flags used Debugger.Launch, which only works on windows. I borrowed the equivalent code from the LSP launcher, which already has this functionality (https://github.com/dotnet/roslyn/blob/cf34acbc5d0f64ff87013cdd02ae61cff562daaf/src/LanguageServer/Microsoft.CodeAnalysis.LanguageServer/Program.cs#L75-L89).

Author: 333fred

src/Compilers/CSharp/Portable/CommandLine/CSharpCommandLineParser.cs

@@ -9,8 +9,10 @@
 using System.Globalization;
 using System.IO;
 using System.Linq;
+using System.Runtime.InteropServices;
 using System.Security.Cryptography;
 using System.Text;
+using System.Threading;
 using Microsoft.CodeAnalysis.Emit;
 using Microsoft.CodeAnalysis.PooledObjects;
 using Microsoft.CodeAnalysis.Text;
@@ -282,7 +284,22 @@ internal sealed override CommandLineArguments CommonParse(IEnumerable<string> ar
 
 #if DEBUG
                     case "attachdebugger":
-                        Debugger.Launch();
+                        if (RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
+                        {
+                            // Debugger.Launch() only works on Windows.
+                            _ = Debugger.Launch();
+                        }
+                        else
+                        {
+                            var timeout = TimeSpan.FromMinutes(2);
+                            Console.WriteLine($"Compiler started with process ID {Environment.ProcessId}");
+                            Console.WriteLine($"Waiting {timeout:g} for a debugger to attach");
+                            using var timeoutSource = new CancellationTokenSource(timeout);
+                            while (!Debugger.IsAttached && !timeoutSource.Token.IsCancellationRequested)
+                            {
+                                Thread.Sleep(100);
+                            }
+                        }
                         continue;
 #endif
                 }

src/Compilers/CSharp/Portable/Utilities/EnvironmentExtensions.cs

@@ -0,0 +1,25 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
+
+namespace Microsoft.CodeAnalysis.CSharp;
+
+internal static class EnvironmentExtensions
+{
+    extension(Environment)
+    {
+        public static int ProcessId
+        {
+            get
+            {
+#if NET
+                return Environment.ProcessId;
+#else
+                return System.Diagnostics.Process.GetCurrentProcess().Id;
+#endif
+            }
+        }
+    }
+}

src/Compilers/VisualBasic/Portable/CommandLine/VisualBasicCommandLineParser.vb

@@ -8,6 +8,7 @@ Imports System.IO
 Imports System.Runtime.InteropServices
 Imports System.Security.Cryptography
 Imports System.Text
+Imports System.Threading
 Imports Microsoft.CodeAnalysis.Collections
 Imports Microsoft.CodeAnalysis.Emit
 Imports Microsoft.CodeAnalysis.PooledObjects
@@ -446,7 +447,24 @@ Namespace Microsoft.CodeAnalysis.VisualBasic
 
 #If DEBUG Then
                     Case "attachdebugger"
-                        Debugger.Launch()
+                        If RuntimeInformation.IsOSPlatform(OSPlatform.Windows) Then
+                            ' Debugger.Launch() only works on Windows
+                            Debugger.Launch()
+                        Else
+                            Dim timeout = TimeSpan.FromMinutes(2)
+#If NET Then
+                            Dim processId = Environment.ProcessId
+#Else
+                            Dim processId = System.Diagnostics.Process.GetCurrentProcess().Id
+#End If
+                            Console.WriteLine($"Compiler started with process ID {processId}")
+                            Console.WriteLine($"Waiting {timeout:g} for a debugger to attach")
+                            Using timeoutSource = New CancellationTokenSource(timeout)
+                                While Not Debugger.IsAttached AndAlso Not timeoutSource.Token.IsCancellationRequested
+                                    Thread.Sleep(100)
+                                End While
+                            End Using
+                        End If
                         Continue For
 #End If
                 End Select