runtime: iOS: building with LLVM causes some exception catch clauses to not work

Description

See the following test code: https://gist.github.com/rolfbjarne/f5c1a3697343c5e9bb6cb8e5b796d328#file-appdelegate-cs-L23-L73

When executed on an iOS device (AOT compiled), this produces the following output:

TCP connection failed when selecting 'hostname': fe80::6aa3:6295:30dd:b552 and 'port': 49681. System.Net.Internals.SocketExceptionFactory+ExtendedSocketException (65): No route to host [fe80::6aa3:6295:30dd:b552]:49681
   at System.Net.Sockets.Socket.DoConnect(EndPoint , SocketAddress ) in System.Net.Sockets.dll:token 0x6000127+0x68
   at System.Net.Sockets.Socket.Connect(EndPoint ) in System.Net.Sockets.dll:token 0x600010a+0xca
   at System.Net.Sockets.Socket.Connect(IPAddress , Int32 ) in System.Net.Sockets.dll:token 0x600010b+0x62
   at System.Net.Sockets.TcpClient.Connect(String , Int32 ) in System.Net.Sockets.dll:token 0x60001b7+0xc7
--- End of stack trace from previous location ---
   at System.Net.Sockets.TcpClient.Connect(String , Int32 ) in System.Net.Sockets.dll:token 0x60001b7+0x158
   at System.Net.Sockets.TcpClient..ctor(String , Int32 ) in System.Net.Sockets.dll:token 0x60001b4+0x56
   at MySingleView.AppDelegate.<>c__DisplayClass3_2.<SelectHostName>b__0(Object v) in /Users/rolf/work/maccore/squashed-onedotnet/xamarin-macios/tests/dotnet/MySingleView/AppDelegate.cs:line 49
[...]
Selected host name: 

if I enable LLVM, the following happens:

Unhandled managed exception: No route to host [fe80::6aa3:6295:30dd:b552]:49681 (System.Net.Internals.SocketExceptionFactory+ExtendedSocketException)
   at System.Threading.QueueUserWorkItemCallbackDefaultContext.Execute()
Unhandled managed exception: No route to host [fe80::14a6:1e61:2f4e:e2c5]:49681 (System.Net.Internals.SocketExceptionFactory+ExtendedSocketException)
   at System.Threading.QueueUserWorkItemCallbackDefaultContext.Execute()

=================================================================
	Native Crash Reporting
=================================================================
Got a SIGABRT while executing native code. This usually indicates
a fatal error in the mono runtime or one of the native libraries 
used by your application.
=================================================================

=================================================================
	Native stacktrace:
=================================================================

It’s a rather strange bug, because in my original test it doesn’t crash this way, the SelectHostName code causes a lot of other test failures due to Assert.Throws<FooException> statements not actually catching the FooException, but then the general NUnit catch handler catches these exceptions, and turn them into test failures. The baffling effect was that running the tests outside of our test harness (without needing to call the SelectHostName method), the tests passed.

In any case, let me know if you can reproduce with this information, or I’ll create a test case you can use (which will likely require building a custom branch of xamarin-macios).