[build] Make sure -mmacosx-version-min is passed to the mono build. Fixes #5553.

Also add a test.

Fixes https://github.com/xamarin/xamarin-macios/issues/5553.

builds/Makefile

@@ -244,7 +244,7 @@ $(2)_CPPFLAGS = \
 	-mmacosx-version-min=$(MIN_OSX_SDK_VERSION)
 $(2)_CFLAGS = -O2 -arch $(1)
 $(2)_CXXFLAGS = -O2 -arch $(1)
-$(2)_LDFLAGS = $(COMMON_LDFLAGS)
+$(2)_LDFLAGS = $(COMMON_LDFLAGS) -mmacosx-version-min=$(MIN_OSX_SDK_VERSION)
 $(2)_CONFIGURE_FLAGS = \
 	--prefix=$$(BUILD_DESTDIR)/$(2) \
 	--host=$(1)-apple-darwin10 \

tests/common/ProductTests.cs

@@ -3,12 +3,16 @@
  **/
 
 using System;
+using System.Collections.Generic;
 using System.IO;
+using System.Linq;
 using System.Xml;
 using System.Text;
 
 using NUnit.Framework;
 
+using Xamarin;
+
 namespace Xamarin.Tests
 {
 	[TestFixture]
@@ -32,6 +36,73 @@ namespace Xamarin.Tests
 				Assert.DoesNotThrow (() => Version.Parse (version), "version");
 			}
 		}
+
+		[Test]
+		[TestCase (Profile.macOSSystem, MachO.LoadCommands.MinMacOSX)]
+		[TestCase (Profile.macOSFull, MachO.LoadCommands.MinMacOSX)]
+		[TestCase (Profile.macOSMobile, MachO.LoadCommands.MinMacOSX)]
+		[TestCase (Profile.iOS, MachO.LoadCommands.MiniPhoneOS, false)]
+		[TestCase (Profile.iOS, MachO.LoadCommands.MiniPhoneOS, true)]
+		[TestCase (Profile.watchOS, MachO.LoadCommands.MinwatchOS, false)]
+		[TestCase (Profile.watchOS, MachO.LoadCommands.MinwatchOS, true)]
+		[TestCase (Profile.tvOS, MachO.LoadCommands.MintvOS, false)]
+		[TestCase (Profile.tvOS, MachO.LoadCommands.MintvOS, true)]
+		public void MinOSVersion (Profile profile, MachO.LoadCommands load_command, bool device = false)
+		{
+			var dylibs = Directory.GetFiles (Configuration.GetSdkPath (profile, device), "*.dylib", SearchOption.AllDirectories)
+				.Where ((v) => !v.Contains ("dylib.dSYM/Contents/Resources/DWARF")); // Don't include *.dylib from inside .dSYMs.
+
+			var failed = new List<string> ();
+			foreach (var dylib in dylibs) {
+				var fatfile = MachO.Read (dylib);
+				foreach (var slice in fatfile) {
+					var any_load_command = false;
+					foreach (var lc in slice.load_commands) {
+						var mincmd = lc as MinCommand;
+						if (mincmd == null)
+							continue;
+						// Console.WriteLine ($"    {mincmd.Command} version: {mincmd.version}=0x{mincmd.version.ToString ("x")}={mincmd.Version} sdk: {mincmd.sdk}=0x{mincmd.sdk.ToString ("x")}={mincmd.Sdk}");
+
+						Assert.AreEqual (load_command, mincmd.Command, "Unexpected min load command");
+
+						Version version;
+						Version alternate_version = null;
+						switch (load_command) {
+						case MachO.LoadCommands.MinMacOSX:
+							version = SdkVersions.MinOSXVersion;
+							break;
+						case MachO.LoadCommands.MiniPhoneOS:
+							version = SdkVersions.MiniOSVersion;
+							if (device) {
+								if (version.Major < 7)
+									version = new Version (7, 0, 0); // dylibs are supported starting with iOS 7.
+								alternate_version = new Version (8, 0, 0); // some iOS dylibs also have min OS 8.0 (if they're used as frameworks as well).
+							}
+							break;
+						case MachO.LoadCommands.MintvOS:
+							version = SdkVersions.MinTVOSVersion;
+							break;
+						case MachO.LoadCommands.MinwatchOS:
+							version = SdkVersions.MinWatchOSVersion;
+							break;
+						default:
+							throw new NotImplementedException (load_command.ToString ());
+						}
+
+						version = new Version (version.Major, version.Minor, version.Build < 0 ? 0 : version.Build);
+						if (alternate_version == null)
+							alternate_version = version;
+
+						if (version != mincmd.Version && alternate_version != mincmd.Version)
+							failed.Add ($"Unexpected minOS version (expected {version}, alternatively {alternate_version}, found {mincmd.Version}) in {dylib}.");
+						any_load_command = true;
+					}
+					if (!any_load_command)
+						failed.Add ($"No minOS version found in {dylib}.");
+				}
+			}
+			CollectionAssert.IsEmpty (failed, "Failures");
+		}
 	}
 }
 

tests/mtouch/mtouch.csproj

@@ -84,6 +84,9 @@
       <Link>ErrorHelper.cs</Link>
     </Compile>
     <Compile Include="RuntimeException.cs" />
+    <Compile Include="..\..\tools\mtouch\SdkVersions.cs">
+      <Link>SdkVersions.cs</Link>
+    </Compile>
   </ItemGroup>
   <ItemGroup>
     <None Include="packages.config" />