[CSSimplify] Skip transitive conformance check if argument is CGFloat

There is an implicit conversion between `CGFloat` and `Double` types
so if `CGFloat` argument doesn't satisfy the requirement it's possible
that the generic parameter it's passed to be inferred as a `Double`
from context and the requirement to be satisfied through this implicit
conversion.

Resolves: rdar://153461854

Author: xedin

lib/Sema/CSSimplify.cpp

@@ -9247,6 +9247,14 @@ ConstraintSystem::SolutionKind ConstraintSystem::simplifyTransitivelyConformsTo(
   if (resolvedTy->isTypeVariableOrMember())
     return formUnsolved();
 
+  // There is an implicit conversion between `CGFloat` and `Double` types
+  // so if `CGFloat` argument doesn't satisfy the requirement it's possible
+  // that the generic parameter it's passed to be inferred as a `Double`
+  // from context and the requirement to be satisfied through this implicit
+  // conversion.
+  if (resolvedTy->isCGFloat())
+    return SolutionKind::Solved;
+
   // If the composition consists of a class + protocol,
   // we can't check conformance of the argument because
   // parameter could pick one of the components.

test/Constraints/transitive_conformances_and_cgfloat.swift

@@ -0,0 +1,18 @@
+// RUN: %empty-directory(%t)
+// RUN: %target-swift-frontend(mock-sdk: %clang-importer-sdk) -typecheck -debug-constraints -verify %s 2>%t.err
+// RUN: %FileCheck %s < %t.err
+
+// rdar://153461854
+
+import CoreGraphics
+
+// There is no better way to check this at the moment because diagnostic mode would produce
+// a valid solution for this example. We need to make sure that the solution is produced in
+// normal mode instead.
+
+ let _ = { (point: CGFloat) in
+   let _: SIMD2<Double>? = SIMD2(point, point)
+ }
+
+// CHECK-NOT: failed constraint CGFloat transitive conformance to SIMDScalar
+// CHECK-NOT: Attempting to salvage