swift234

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

Stack trace:

```
4  swift           0x0000000000ed9e0a swift::TypeChecker::checkGenericParamList(swift::ArchetypeBuilder*, swift::GenericParamList*, swift::GenericSignature*, bool, swift::GenericTypeResolver*) + 74
5  swift           0x0000000000edb637 swift::TypeChecker::validateGenericSignature(swift::GenericParamList*, swift::DeclContext*, swift::GenericSignature*, std::function<bool (swift::ArchetypeBuilder&)>, bool&) + 135
6  swift           0x0000000000edb9d6 swift::TypeChecker::validateGenericTypeSignature(swift::GenericTypeDecl*) + 102
7  swift           0x0000000000e9c94f swift::TypeChecker::validateDecl(swift::ValueDecl*, bool) + 367
12 swift           0x0000000000ea2166 swift::TypeChecker::typeCheckDecl(swift::Decl*, bool) + 150
13 swift           0x0000000000ec4ac2 swift::performTypeChecking(swift::SourceFile&, swift::TopLevelContext&, swift::OptionSet<swift::TypeCheckingFlags, unsigned int>, unsigned int, unsigned int) + 1026
14 swift           0x0000000000c58d39 swift::CompilerInstance::performSema() + 3289
16 swift           0x00000000007d73bf swift::performFrontend(llvm::ArrayRef<char const*>, char const*, void*, swift::FrontendObserver*) + 2863
17 swift           0x00000000007a33d8 main + 2872
Stack dump:
0.	Program arguments: /path/to/swift/bin/swift -frontend -c -primary-file validation-test/compiler_crashers/28308-swift-typechecker-checkgenericparamlist.swift -target x86_64-unknown-linux-gnu -disable-objc-interop -module-name main -o /tmp/28308-swift-typechecker-checkgenericparamlist-b4f9c8.o
1.	While type-checking 'B' at validation-test/compiler_crashers/28308-swift-typechecker-checkgenericparamlist.swift:9:1
<unknown>:0: error: unable to execute command: Segmentation fault
<unknown>:0: error: compile command failed due to signal (use -v to see invocation)
```