SIL verification failure of key paths, only on Windows

[ahoppen]

CI testing of the following PR gives me a SIL verification failure on Windows only. The build works fine on macOS and Linux. swiftlang/swift-syntax#1921

SIL verification failed: operand must match type required by pattern

Verifying instruction:
     %5 = alloc_stack $SyntaxChildrenIndex        // users: %9, %7, %6
->   %7 = keypath $WritableKeyPath<Self, Self.Element>, <Ï„_0_0 where Ï„_0_0 : SyntaxCollection> (root $Ï„_0_0; settable_property $Ï„_0_0.Element,  id @$s11SwiftSyntax0B10CollectionPAAEy7ElementQzAA0B13ChildrenIndexVcig : $@convention(method) <Ï„_0_0 where Ï„_0_0 : SyntaxCollection> (@in_guaranteed SyntaxChildrenIndex, @in_guaranteed Ï„_0_0) -> @out Ï„_0_0.Element, getter @$s11SwiftSyntax0B10CollectionPAAEy7ElementQzAA0B13ChildrenIndexVcipAaBRzlxxTK : $@convention(thin) <Ï„_0_0 where Ï„_0_0 : SyntaxCollection> (@in_guaranteed Ï„_0_0, UnsafeRawPointer) -> @out Ï„_0_0.Element, setter @$s11SwiftSyntax0B10CollectionPAAEy7ElementQzAA0B13ChildrenIndexVcipAaBRzlxxTk : $@convention(thin) <Ï„_0_0 where Ï„_0_0 : SyntaxCollection> (@in_guaranteed Ï„_0_0.Element, @inout Ï„_0_0, UnsafeRawPointer) -> (), indices [%$0 : $SyntaxChildrenIndex : $SyntaxChildrenIndex], indices_equals @$s11SwiftSyntax0B13ChildrenIndexVAA0B10CollectionRzlTH : $@convention(thin) <Ï„_0_0 where Ï„_0_0 : SyntaxCollection> (UnsafeRawPointer, UnsafeRawPointer) -> Bool, indices_hash @$s11SwiftSyntax0B13ChildrenIndexVAA0B10CollectionRzlTh : $@convention(thin) <Ï„_0_0 where Ï„_0_0 : SyntaxCollection> (UnsafeRawPointer) -> Int) <Self> (%5) // user: %8
     %8 = upcast %7 : $WritableKeyPath<Self, Self.Element> to $AnyKeyPath // user: %10
In function:
// SyntaxCollection.keyPath(for:)
sil private [ossa] @$s11SwiftSyntax0B10CollectionPAAE7keyPath33_B3300DB0BA2B3E5E35A338B811650793LL3fors06AnyKeyE0CAA0B13ChildrenIndexV_tF : $@convention(method) <Self where Self : SyntaxCollection> (@in_guaranteed SyntaxChildrenIndex, @in_guaranteed Self) -> @owned AnyKeyPath {
// %0 "index"                                     // user: %2
// %1 "self"                                      // user: %4
bb0(%0 : $*SyntaxChildrenIndex, %1 : $*Self):
  %2 = load [trivial] %0 : $*SyntaxChildrenIndex  // users: %6, %3
  debug_value %2 : $SyntaxChildrenIndex, let, name "index", argno 1 // id: %3
  debug_value %1 : $*Self, let, name "self", argno 2, implicit, expr op_deref // id: %4
  %5 = alloc_stack $SyntaxChildrenIndex           // users: %9, %7, %6
  store %2 to [trivial] %5 : $*SyntaxChildrenIndex // id: %6
  %7 = keypath $WritableKeyPath<Self, Self.Element>, <Ï„_0_0 where Ï„_0_0 : SyntaxCollection> (root $Ï„_0_0; settable_property $Ï„_0_0.Element,  id @$s11SwiftSyntax0B10CollectionPAAEy7ElementQzAA0B13ChildrenIndexVcig : $@convention(method) <Ï„_0_0 where Ï„_0_0 : SyntaxCollection> (@in_guaranteed SyntaxChildrenIndex, @in_guaranteed Ï„_0_0) -> @out Ï„_0_0.Element, getter @$s11SwiftSyntax0B10CollectionPAAEy7ElementQzAA0B13ChildrenIndexVcipAaBRzlxxTK : $@convention(thin) <Ï„_0_0 where Ï„_0_0 : SyntaxCollection> (@in_guaranteed Ï„_0_0, UnsafeRawPointer) -> @out Ï„_0_0.Element, setter @$s11SwiftSyntax0B10CollectionPAAEy7ElementQzAA0B13ChildrenIndexVcipAaBRzlxxTk : $@convention(thin) <Ï„_0_0 where Ï„_0_0 : SyntaxCollection> (@in_guaranteed Ï„_0_0.Element, @inout Ï„_0_0, UnsafeRawPointer) -> (), indices [%$0 : $SyntaxChildrenIndex : $SyntaxChildrenIndex], indices_equals @$s11SwiftSyntax0B13ChildrenIndexVAA0B10CollectionRzlTH : $@convention(thin) <Ï„_0_0 where Ï„_0_0 : SyntaxCollection> (UnsafeRawPointer, UnsafeRawPointer) -> Bool, indices_hash @$s11SwiftSyntax0B13ChildrenIndexVAA0B10CollectionRzlTh : $@convention(thin) <Ï„_0_0 where Ï„_0_0 : SyntaxCollection> (UnsafeRawPointer) -> Int) <Self> (%5) // user: %8
  %8 = upcast %7 : $WritableKeyPath<Self, Self.Element> to $AnyKeyPath // user: %10
  dealloc_stack %5 : $*SyntaxChildrenIndex        // id: %9
  return %8 : $AnyKeyPath                         // id: %10
} // end sil function '$s11SwiftSyntax0B10CollectionPAAE7keyPath33_B3300DB0BA2B3E5E35A338B811650793LL3fors06AnyKeyE0CAA0B13ChildrenIndexV_tF

rdar://112552022