[macos] Add unsupported force-unsupported-linker option to mmp (#2449)

- This option disables the check that prevents linking on non-modern profiles
- Due to System.Configuration, this is unsafe in general. It may cause assorted runtime crashes.

tests/mmptest/src/MMPTest.cs

@@ -714,6 +714,20 @@ namespace Xamarin.MMP.Tests
 				TI.TestUnifiedExecutable (test);
 			});
 		}
-		
+
+		[Test]
+		public void UnifiedFull_AllowsLinking_WithForceFlag ()
+		{
+			RunMMPTest (tmpDir => {
+				TI.UnifiedTestConfig test = new TI.UnifiedTestConfig (tmpDir) {
+					XM45 = true,
+					CSProjConfig = "<LinkMode>Full</LinkMode>"
+				};
+				TI.TestUnifiedExecutable (test, shouldFail: true);
+
+				test.CSProjConfig = test.CSProjConfig + "<MonoBundlingExtraArgs>--force-unsupported-linker</MonoBundlingExtraArgs>";
+				TI.TestUnifiedExecutable (test);
+			});
+		}
 	}
 }

tools/mmp/driver.cs

@@ -90,6 +90,7 @@ namespace Xamarin.Bundler {
 		static LinkerOptions linker_options;
 		static bool? disable_lldb_attach = null;
 		static string machine_config_path = null;
+		static bool bypass_linking_checks = false;
 
 		static bool arch_set = false;
 		static string arch = "i386";
@@ -348,6 +349,7 @@ namespace Xamarin.Bundler {
 				{ "http-message-handler=", "Specify the default HTTP Message Handler", v => { http_message_provider = v; }},
 				{ "extension", "Specifies an app extension", v => is_extension = true },
 				{ "allow-unsafe-gac-resolution", "Allow MSBuild to resolve from the System GAC", v => {} , true }, // Used in Xamarin.Mac.XM45.targets and must be ignored here. Hidden since it is a total hack. If you can use it, you don't need support
+				{ "force-unsupported-linker", "Bypass safety checkes preventing unsupported linking options.", v => bypass_linking_checks = true , true }, // Undocumented option for a reason, You get to keep the pieces when it breaks
 				{ "disable-lldb-attach=", "Disable automatic lldb attach on crash", v => disable_lldb_attach = ParseBool (v, "disable-lldb-attach")},
 				{ "machine-config=", "Custom machine.config file to copy into MonoBundle/mono/4.5/machine.config. Pass \"\" to copy in a valid \"empty\" config file.", v => machine_config_path = v },
 				{ "runregistrar:", "Runs the registrar on the input assembly and outputs a corresponding native library.",
@@ -482,7 +484,7 @@ namespace Xamarin.Bundler {
 				throw new Exception ("IsClassic/IsUnified/IsUnifiedMobile/IsUnifiedFullSystemFramework/IsUnifiedFullXamMacFramework logic regression");
 
 			ValidateXamarinMacReference ();
-			if (IsUnifiedFullSystemFramework || IsUnifiedFullXamMacFramework) {
+			if (!bypass_linking_checks && (IsUnifiedFullSystemFramework || IsUnifiedFullXamMacFramework)) {
 				switch (App.LinkMode) {
 				case LinkMode.None:
 				case LinkMode.Platform: