[swiftc] Add test case for crash triggered in swift::TypeChecker::checkGenericParamList(swift::ArchetypeBuilder*, swift::GenericParamList*, swift::GenericSignature*, bool, swift::GenericTypeResolver*)

Stack trace:

```
4  swift           0x0000000000ed889d swift::TypeChecker::checkGenericParamList(swift::ArchetypeBuilder*, swift::GenericParamList*, swift::GenericSignature*, bool, swift::GenericTypeResolver*) + 93
5  swift           0x0000000000eda0b7 swift::TypeChecker::validateGenericSignature(swift::GenericParamList*, swift::DeclContext*, swift::GenericSignature*, std::function<bool (swift::ArchetypeBuilder&)>, bool&) + 135
6  swift           0x0000000000eda456 swift::TypeChecker::validateGenericTypeSignature(swift::GenericTypeDecl*) + 102
7  swift           0x0000000000e9b34f swift::TypeChecker::validateDecl(swift::ValueDecl*, bool) + 367
8  swift           0x00000000010f4c5c swift::DeclContext::lookupQualified(swift::Type, swift::DeclName, swift::NLOptions, swift::LazyResolver*, llvm::SmallVectorImpl<swift::ValueDecl*>&) const + 2652
9  swift           0x0000000000edce17 swift::TypeChecker::lookupMemberType(swift::DeclContext*, swift::Type, swift::Identifier, swift::OptionSet<swift::NameLookupFlags, unsigned int>) + 295
12 swift           0x0000000000ee6aaf swift::TypeChecker::checkConformance(swift::NormalProtocolConformance*) + 1631
13 swift           0x0000000000ee71a7 swift::TypeChecker::checkConformancesInContext(swift::DeclContext*, swift::IterableDeclContext*) + 471
16 swift           0x0000000000ea0b66 swift::TypeChecker::typeCheckDecl(swift::Decl*, bool) + 150
19 swift           0x0000000000f05f8a swift::TypeChecker::typeCheckFunctionBodyUntil(swift::FuncDecl*, swift::SourceLoc) + 346
20 swift           0x0000000000f05dee swift::TypeChecker::typeCheckAbstractFunctionBodyUntil(swift::AbstractFunctionDecl*, swift::SourceLoc) + 46
21 swift           0x0000000000f069b3 swift::TypeChecker::typeCheckAbstractFunctionBody(swift::AbstractFunctionDecl*) + 179
23 swift           0x0000000000ec3641 swift::performTypeChecking(swift::SourceFile&, swift::TopLevelContext&, swift::OptionSet<swift::TypeCheckingFlags, unsigned int>, unsigned int, unsigned int) + 1281
24 swift           0x0000000000c58089 swift::CompilerInstance::performSema() + 3289
26 swift           0x00000000007d7409 swift::performFrontend(llvm::ArrayRef<char const*>, char const*, void*, swift::FrontendObserver*) + 2857
27 swift           0x00000000007a3428 main + 2872
Stack dump:
0.	Program arguments: /path/to/swift/bin/swift -frontend -c -primary-file validation-test/compiler_crashers/28311-swift-typechecker-checkgenericparamlist.swift -target x86_64-unknown-linux-gnu -disable-objc-interop -module-name main -o /tmp/28311-swift-typechecker-checkgenericparamlist-bbd21e.o
1.	While type-checking 'b' at validation-test/compiler_crashers/28311-swift-typechecker-checkgenericparamlist.swift:10:24
2.	While type-checking 'b' at validation-test/compiler_crashers/28311-swift-typechecker-checkgenericparamlist.swift:10:33
<unknown>:0: error: unable to execute command: Segmentation fault
<unknown>:0: error: compile command failed due to signal (use -v to see invocation)
```

Author: practicalswift

validation-test/compiler_crashers/28311-swift-typechecker-checkgenericparamlist.swift

@@ -0,0 +1,10 @@
+// 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
+// REQUIRES: asserts
+protocol P{typealias e}func b(){class b:P{enum e where g:b