Add 💥 (😢 → 61, 😀 → 5107) in swift::constraints::ConstraintSystem::add…

…TypeVariableConstraintsToWorkList(…)

Add test case for crash triggered in `swift::constraints::ConstraintSystem::addTypeVariableConstraintsToWorkList(…)`.

<details>
<summary>Stack trace:</summary>
```
4  swift           0x0000000000f3b8e1 swift::constraints::ConstraintSystem::addTypeVariableConstraintsToWorkList(swift::TypeVariableType*) + 113
5  swift           0x0000000000f3bae9 swift::constraints::ConstraintSystem::assignFixedType(swift::TypeVariableType*, swift::Type, bool) + 377
6  swift           0x0000000000fabea8 swift::constraints::ConstraintSystem::finalize(swift::FreeTypeVariableBinding) + 792
7  swift           0x0000000000fb5933 swift::constraints::ConstraintSystem::solveSimplified(llvm::SmallVectorImpl<swift::constraints::Solution>&, swift::FreeTypeVariableBinding) + 11843
8  swift           0x0000000000fb11d5 swift::constraints::ConstraintSystem::solveRec(llvm::SmallVectorImpl<swift::constraints::Solution>&, swift::FreeTypeVariableBinding) + 325
9  swift           0x0000000000fb4ec3 swift::constraints::ConstraintSystem::solveSimplified(llvm::SmallVectorImpl<swift::constraints::Solution>&, swift::FreeTypeVariableBinding) + 9171
10 swift           0x0000000000fb11d5 swift::constraints::ConstraintSystem::solveRec(llvm::SmallVectorImpl<swift::constraints::Solution>&, swift::FreeTypeVariableBinding) + 325
11 swift           0x0000000000fb4ec3 swift::constraints::ConstraintSystem::solveSimplified(llvm::SmallVectorImpl<swift::constraints::Solution>&, swift::FreeTypeVariableBinding) + 9171
12 swift           0x0000000000fb1d29 swift::constraints::ConstraintSystem::solveRec(llvm::SmallVectorImpl<swift::constraints::Solution>&, swift::FreeTypeVariableBinding) + 3225
13 swift           0x0000000000fb3840 swift::constraints::ConstraintSystem::solveSimplified(llvm::SmallVectorImpl<swift::constraints::Solution>&, swift::FreeTypeVariableBinding) + 3408
14 swift           0x0000000000fb11d5 swift::constraints::ConstraintSystem::solveRec(llvm::SmallVectorImpl<swift::constraints::Solution>&, swift::FreeTypeVariableBinding) + 325
15 swift           0x0000000000fb0f89 swift::constraints::ConstraintSystem::solve(llvm::SmallVectorImpl<swift::constraints::Solution>&, swift::FreeTypeVariableBinding) + 73
16 swift           0x0000000000e9b6d0 swift::TypeChecker::solveForExpression(swift::Expr*&, swift::DeclContext*, swift::Type, swift::FreeTypeVariableBinding, swift::ExprTypeCheckListener*, swift::constraints::ConstraintSystem&, llvm::SmallVectorImpl<swift::constraints::Solution>&, swift::OptionSet<swift::TypeCheckExprFlags, unsigned int>) + 800
17 swift           0x0000000000ea1e62 swift::TypeChecker::typeCheckExpression(swift::Expr*&, swift::DeclContext*, swift::TypeLoc, swift::ContextualTypePurpose, swift::OptionSet<swift::TypeCheckExprFlags, unsigned int>, swift::ExprTypeCheckListener*) + 610
20 swift           0x0000000000f63cb9 swift::constraints::ConstraintSystem::diagnoseFailureForExpr(swift::Expr*) + 105
21 swift           0x0000000000f6963e swift::constraints::ConstraintSystem::salvage(llvm::SmallVectorImpl<swift::constraints::Solution>&, swift::Expr*) + 3998
22 swift           0x0000000000e9b702 swift::TypeChecker::solveForExpression(swift::Expr*&, swift::DeclContext*, swift::Type, swift::FreeTypeVariableBinding, swift::ExprTypeCheckListener*, swift::constraints::ConstraintSystem&, llvm::SmallVectorImpl<swift::constraints::Solution>&, swift::OptionSet<swift::TypeCheckExprFlags, unsigned int>) + 850
23 swift           0x0000000000ea1e62 swift::TypeChecker::typeCheckExpression(swift::Expr*&, swift::DeclContext*, swift::TypeLoc, swift::ContextualTypePurpose, swift::OptionSet<swift::TypeCheckExprFlags, unsigned int>, swift::ExprTypeCheckListener*) + 610
26 swift           0x0000000000f19dea swift::TypeChecker::typeCheckFunctionBodyUntil(swift::FuncDecl*, swift::SourceLoc) + 346
27 swift           0x0000000000f19c4e swift::TypeChecker::typeCheckAbstractFunctionBodyUntil(swift::AbstractFunctionDecl*, swift::SourceLoc) + 46
28 swift           0x0000000000f1a813 swift::TypeChecker::typeCheckAbstractFunctionBody(swift::AbstractFunctionDecl*) + 179
30 swift           0x0000000000ed5b01 swift::performTypeChecking(swift::SourceFile&, swift::TopLevelContext&, swift::OptionSet<swift::TypeCheckingFlags, unsigned int>, unsigned int, unsigned int) + 1281
31 swift           0x0000000000c62229 swift::CompilerInstance::performSema() + 3289
33 swift           0x00000000007d85a9 swift::performFrontend(llvm::ArrayRef<char const*>, char const*, void*, swift::FrontendObserver*) + 2857
34 swift           0x00000000007a45c8 main + 2872
Stack dump:
0.	Program arguments: /path/to/swift/bin/swift -frontend -c -primary-file validation-test/compiler_crashers/28359-swift-constraints-constraintsystem-addtypevariableconstraintstoworklist.swift -target x86_64-unknown-linux-gnu -disable-objc-interop -module-name main -o /tmp/28359-swift-constraints-constraintsystem-addtypevariableconstraintstoworklist-e0b297.o
1.	While type-checking 'b' at validation-test/compiler_crashers/28359-swift-constraints-constraintsystem-addtypevariableconstraintstoworklist.swift:9:28
2.	While type-checking expression at [validation-test/compiler_crashers/28359-swift-constraints-constraintsystem-addtypevariableconstraintstoworklist.swift:9:35 - line:9:40] RangeText="{{a(a{"
3.	While type-checking expression at [validation-test/compiler_crashers/28359-swift-constraints-constraintsystem-addtypevariableconstraintstoworklist.swift:9:36 - line:9:40] RangeText="{a(a{"
<unknown>:0: error: unable to execute command: Segmentation fault
<unknown>:0: error: compile command failed due to signal (use -v to see invocation)
```
</details>

validation-test/compiler_crashers/28359-swift-constraints-constraintsystem-addtypevariableconstraintstoworklist.swift

@@ -0,0 +1,9 @@
+// This source file is part of the Swift.org open source project
+// Copyright (c) 2014 - 2016 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See http://swift.org/LICENSE.txt for license information
+// See http://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+
+// RUN: not --crash %target-swift-frontend %s -parse
+{class a{}func a(a)class c{func b{{{a(a{