[bcl] Fix races in task tests.
Fix win32 build.

This commit licensed as MIT/X11.
[threadpool] Fix deadlock/starvation of the thread pool

The issue was with the new heuristic of the thread pool which would not create new threads, leading to deadlock between dependent tasks.
The fix is to check if every worker threads are sleeping, waiting or joining, and if that's the case, then we create a new thread because we might be in the case where the tasks being currently run depends on one still being enqueued in the cq or one of the wsq.

The following tests would previously fail :

1) MonoTests.System.Threading.Tasks.TaskTests.DoubleWaitTest :   #1
  Expected: True
  But was:  False

at MonoTests.System.Threading.Tasks.TaskTests.<DoubleWaitTest>m__27 () [0x00077] in /Users/ludovic/Xamarin/mono/mcs/class/corlib/Test/System.Threading.Tasks/TaskTest.cs:800
at MonoTests.System.Threading.Tasks.ParallelTestHelper.Repeat (System.Action action, Int32 numRun) [0x00007] in /Users/ludovic/Xamarin/mono/mcs/class/corlib/Test/System.Threading.Tasks/ParallelTestHelper.cs:48
at MonoTests.System.Threading.Tasks.TaskTests.DoubleWaitTest () [0x00000] in /Users/ludovic/Xamarin/mono/mcs/class/corlib/Test/System.Threading.Tasks/TaskTest.cs:790
at (wrapper managed-to-native) System.Reflection.MonoMethod:InternalInvoke (System.Reflection.MonoMethod,object,object[],System.Exception&)
at System.Reflection.MonoMethod.Invoke (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) [0x00054] in /Users/ludovic/Xamarin/mono/mcs/class/corlib/System.Reflection/MonoMethod.cs:230

2) MonoTests.System.Threading.Tasks.TaskTests.HideSchedulerTest :   #1
  Expected: True
  But was:  False

at MonoTests.System.Threading.Tasks.TaskTests.HideSchedulerTest () [0x0003d] in /Users/ludovic/Xamarin/mono/mcs/class/corlib/Test/System.Threading.Tasks/TaskTest.cs:1914
at (wrapper managed-to-native) System.Reflection.MonoMethod:InternalInvoke (System.Reflection.MonoMethod,object,object[],System.Exception&)
at System.Reflection.MonoMethod.Invoke (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) [0x00054] in /Users/ludovic/Xamarin/mono/mcs/class/corlib/System.Reflection/MonoMethod.cs:230

3) MonoTests.System.Threading.Tasks.TaskTests.WaitAll_TimeoutWithExceptionsAfter :   #1
  Expected: True
  But was:  False

at MonoTests.System.Threading.Tasks.TaskTests.WaitAll_TimeoutWithExceptionsAfter () [0x00070] in /Users/ludovic/Xamarin/mono/mcs/class/corlib/Test/System.Threading.Tasks/TaskTest.cs:317
at (wrapper managed-to-native) System.Reflection.MonoMethod:InternalInvoke (System.Reflection.MonoMethod,object,object[],System.Exception&)
at System.Reflection.MonoMethod.Invoke (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) [0x00054] in /Users/ludovic/Xamarin/mono/mcs/class/corlib/System.Reflection/MonoMethod.cs:230

4) MonoTests.System.Threading.Tasks.TaskTests.WaitAll_TimeoutWithExceptionsBefore :   #1
  Expected: True
  But was:  False

at MonoTests.System.Threading.Tasks.TaskTests.WaitAll_TimeoutWithExceptionsBefore () [0x00070] in /Users/ludovic/Xamarin/mono/mcs/class/corlib/Test/System.Threading.Tasks/TaskTest.cs:341
at (wrapper managed-to-native) System.Reflection.MonoMethod:InternalInvoke (System.Reflection.MonoMethod,object,object[],System.Exception&)
at System.Reflection.MonoMethod.Invoke (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) [0x00054] in /Users/ludovic/Xamarin/mono/mcs/class/corlib/System.Reflection/MonoMethod.cs:230

5) MonoTests.System.Threading.Tasks.TaskTests.WaitAnyTest :   #3
  Expected: not -1
  But was:  -1

at MonoTests.System.Threading.Tasks.TaskTests.<WaitAnyTest>m__0 () [0x00026] in /Users/ludovic/Xamarin/mono/mcs/class/corlib/Test/System.Threading.Tasks/TaskTest.cs:142
at MonoTests.System.Threading.Tasks.ParallelTestHelper.Repeat (System.Action action, Int32 numRun) [0x00007] in /Users/ludovic/Xamarin/mono/mcs/class/corlib/Test/System.Threading.Tasks/ParallelTestHelper.cs:48
at MonoTests.System.Threading.Tasks.ParallelTestHelper.Repeat (System.Action action) [0x00000] in /Users/ludovic/Xamarin/mono/mcs/class/corlib/Test/System.Threading.Tasks/ParallelTestHelper.cs:42
at MonoTests.System.Threading.Tasks.TaskTests.WaitAnyTest () [0x00000] in /Users/ludovic/Xamarin/mono/mcs/class/corlib/Test/System.Threading.Tasks/TaskTest.cs:128
at (wrapper managed-to-native) System.Reflection.MonoMethod:InternalInvoke (System.Reflection.MonoMethod,object,object[],System.Exception&)
at System.Reflection.MonoMethod.Invoke (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) [0x00054] in /Users/ludovic/Xamarin/mono/mcs/class/corlib/System.Reflection/MonoMethod.cs:230

6) MonoTests.System.Threading.Tasks.TaskTests.WaitChildTestCase :   #0b
  Expected: True
  But was:  False

at MonoTests.System.Threading.Tasks.TaskTests.<WaitChildTestCase>m__25 () [0x0006d] in /Users/ludovic/Xamarin/mono/mcs/class/corlib/Test/System.Threading.Tasks/TaskTest.cs:705
at MonoTests.System.Threading.Tasks.ParallelTestHelper.Repeat (System.Action action, Int32 numRun) [0x00007] in /Users/ludovic/Xamarin/mono/mcs/class/corlib/Test/System.Threading.Tasks/ParallelTestHelper.cs:48
at MonoTests.System.Threading.Tasks.TaskTests.WaitChildTestCase () [0x00000] in /Users/ludovic/Xamarin/mono/mcs/class/corlib/Test/System.Threading.Tasks/TaskTest.cs:684
at (wrapper managed-to-native) System.Reflection.MonoMethod:InternalInvoke (System.Reflection.MonoMethod,object,object[],System.Exception&)
at System.Reflection.MonoMethod.Invoke (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) [0x00054] in /Users/ludovic/Xamarin/mono/mcs/class/corlib/System.Reflection/MonoMethod.cs:230

7) MonoTests.System.Threading.Tasks.TaskTests.WaitingForChildrenToComplete :   #3
  Expected: True
  But was:  False

at MonoTests.System.Threading.Tasks.TaskTests.WaitingForChildrenToComplete () [0x00048] in /Users/ludovic/Xamarin/mono/mcs/class/corlib/Test/System.Threading.Tasks/TaskTest.cs:734
at (wrapper managed-to-native) System.Reflection.MonoMethod:InternalInvoke (System.Reflection.MonoMethod,object,object[],System.Exception&)
at System.Reflection.MonoMethod.Invoke (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) [0x00054] in /Users/ludovic/Xamarin/mono/mcs/class/corlib/System.Reflection/MonoMethod.cs:230
[llvm] Rewrite the way direct calls are made between llvm methods. Previously all calls were made to plt entries and the plt entry symbols were aliased to point to the corresponding method if the method was directly callable using the .set assembler directive. This doesn't seem to work with newer LLVM/CLANG versions, so do this completely on the LLVM side using Value::replaceAllUsesWith (). Fixes #23976.
Merge pull request #1358 from madewokherd/win32build

Fix win32 build.
[runtime] Add checks for overlapping reference and non-reference fields when using explicit layout. Fixes #23954.
[bcl] Restore ThreadPool number of threads configuration after each test