[ConstraintSystem] Fail ~= synthesis if constraint generation fails

If constraint generation for application of `~=` failed that should
result in an immediate synthesis failure.

Resolves: rdar://92366212
(cherry picked from commit 48e70ed)

Author: xedin

lib/Sema/CSSimplify.cpp

@@ -8967,7 +8967,8 @@ static bool inferEnumMemberThroughTildeEqualsOperator(
     }
   }
 
-  cs.generateConstraints(target, FreeTypeVariableBinding::Disallow);
+  if (cs.generateConstraints(target, FreeTypeVariableBinding::Disallow))
+    return true;
 
   // Sub-expression associated with expression pattern is the enum element
   // access which needs to be connected to the provided element type.

test/expr/closure/multi_statement.swift

@@ -316,3 +316,16 @@ func test_wrapped_var_without_initializer() {
     var v;
   }
 }
+
+// rdar://92366212 - crash in ConstraintSystem::getType
+func test_unknown_refs_in_tilde_operator() {
+  enum E {
+  }
+
+  let _: (E) -> Void = {
+    if case .test(unknown) = $0 {
+      // expected-error@-1 {{type 'E' has no member 'test'}}
+      // expected-error@-2 2 {{cannot find 'unknown' in scope}}
+    }
+  }
+}