[mtouch] Add support for -j X to specify concurrency. (#876)

tools/mtouch/Application.cs

@@ -1698,7 +1698,7 @@ namespace Xamarin.Bundler {
 		{
 			var next = v.Execute ();
 			if (next != null)
-				Parallel.ForEach (next, new ParallelOptions () { MaxDegreeOfParallelism = Environment.ProcessorCount }, Execute);
+				Parallel.ForEach (next, new ParallelOptions () { MaxDegreeOfParallelism = Driver.Concurrency }, Execute);
 		}
 
 		public void ExecuteInParallel ()
@@ -1706,7 +1706,7 @@ namespace Xamarin.Bundler {
 			if (Count == 0)
 				return;
 			
-			Parallel.ForEach (this, new ParallelOptions () { MaxDegreeOfParallelism = Environment.ProcessorCount }, Execute);
+			Parallel.ForEach (this, new ParallelOptions () { MaxDegreeOfParallelism = Driver.Concurrency }, Execute);
 
 			Clear ();
 		}

tools/mtouch/Target.cs

@@ -1009,7 +1009,7 @@ namespace Xamarin.Bundler
 
 			if (strip) {
 				// note: this is much slower when Parallel.ForEach is used
-				Parallel.ForEach (Assemblies, new ParallelOptions () { MaxDegreeOfParallelism = Environment.ProcessorCount }, (assembly) => 
+				Parallel.ForEach (Assemblies, new ParallelOptions () { MaxDegreeOfParallelism = Driver.Concurrency }, (assembly) => 
 					{
 						var file = assembly.FullPath;
 						var output = Path.Combine (AppTargetDirectory, Path.GetFileName (assembly.FullPath));

tools/mtouch/mtouch.cs

@@ -150,6 +150,13 @@ namespace Xamarin.Bundler
 
 		public static List<string> classic_only_arguments = new List<string> (); // list of deprecated arguments, which (if used) will cause errors in Unified profile)
 
+		static int Jobs;
+		public static int Concurrency {
+			get {
+				return Jobs == 0 ? Environment.ProcessorCount : Jobs;
+			}
+		}
+
 		//
 		// We need to put a hard dep on Mono.Cecil.Mdb.dll so that it get's mkbundled
 		//
@@ -1075,6 +1082,7 @@ namespace Xamarin.Bundler
 			var os = new OptionSet () {
 			{ "h|?|help", "Displays the help", v => SetAction (Action.Help) },
 			{ "version", "Output version information and exit.", v => SetAction (Action.Version) },
+			{ "j|jobs=", "The level of concurrency. Default is the number of processors.", v => Jobs = int.Parse (v) },
 			{ "d|dir=", "Output directory for the results (Used for partial builds) [Deprecated]", v => { output_dir = v; classic_only_arguments.Add ("--dir"); }, true },
 			{ "cp=|crossprefix=", "Specifies the Mono cross compiler prefix [Deprecated]", v => { cross_prefix = v; classic_only_arguments.Add ("--crossprefix"); }, true },
 			{ "f|force", "Forces the recompilation of code, regardless of timestamps", v=>force = true },