swift234

[swiftc] Add test case for crash triggered in swift::ParamDecl::createUnboundSelf(swift::SourceLoc, swift::DeclContext*, bool, bool)

Stack trace:

```
swift: /path/to/llvm/include/llvm/ADT/ArrayRef.h:265: T &llvm::MutableArrayRef<swift::GenericTypeParamDecl *>::front() const [T = swift::GenericTypeParamDecl *]: Assertion `!this->empty()' failed.
9  swift           0x00000000010b835b swift::ParamDecl::createUnboundSelf(swift::SourceLoc, swift::DeclContext*, bool, bool) + 75
10 swift           0x00000000010f6ff3 swift::ParameterList::createUnboundSelf(swift::SourceLoc, swift::DeclContext*, bool, bool) + 19
11 swift           0x0000000000e606b6 swift::Parser::parseDeclFunc(swift::SourceLoc, swift::StaticSpellingKind, swift::OptionSet<swift::Parser::ParseDeclFlags, unsigned int>, swift::DeclAttributes&) + 3798
12 swift           0x0000000000e562e0 swift::Parser::parseDecl(swift::OptionSet<swift::Parser::ParseDeclFlags, unsigned int>, llvm::function_ref<void (swift::Decl*)>) + 3760
14 swift           0x0000000000e0a4a9 swift::Parser::parseList(swift::tok, swift::SourceLoc, swift::SourceLoc&, swift::tok, bool, bool, swift::Diag<>, std::function<swift::ParserStatus ()>) + 377
15 swift           0x0000000000e5e188 swift::Parser::parseDeclProtocol(swift::OptionSet<swift::Parser::ParseDeclFlags, unsigned int>, swift::DeclAttributes&) + 1656
16 swift           0x0000000000e56373 swift::Parser::parseDecl(swift::OptionSet<swift::Parser::ParseDeclFlags, unsigned int>, llvm::function_ref<void (swift::Decl*)>) + 3907
18 swift           0x0000000000e0a4a9 swift::Parser::parseList(swift::tok, swift::SourceLoc, swift::SourceLoc&, swift::tok, bool, bool, swift::Diag<>, std::function<swift::ParserStatus ()>) + 377
19 swift           0x0000000000e5c458 swift::Parser::parseDeclStruct(swift::OptionSet<swift::Parser::ParseDeclFlags, unsigned int>, swift::DeclAttributes&) + 1848
20 swift           0x0000000000e5638c swift::Parser::parseDecl(swift::OptionSet<swift::Parser::ParseDeclFlags, unsigned int>, llvm::function_ref<void (swift::Decl*)>) + 3932
21 swift           0x0000000000e386b2 swift::Parser::parseBraceItems(llvm::SmallVectorImpl<swift::ASTNode>&, swift::BraceItemListKind, swift::BraceItemListKind) + 850
22 swift           0x0000000000e4a8ac swift::Parser::parseTopLevel() + 156
23 swift           0x0000000000e06920 swift::parseIntoSourceFile(swift::SourceFile&, unsigned int, bool*, swift::SILParserState*, swift::PersistentParserState*, swift::DelayedParsingCallbacks*) + 208
24 swift           0x0000000000c585c6 swift::CompilerInstance::performSema() + 3254
26 swift           0x00000000007d6f4f swift::performFrontend(llvm::ArrayRef<char const*>, char const*, void*, swift::FrontendObserver*) + 2863
27 swift           0x00000000007a2f58 main + 2872
Stack dump:
0.	Program arguments: /path/to/swift/bin/swift -frontend -c -primary-file validation-test/compiler_crashers/28302-swift-paramdecl-createunboundself.swift -target x86_64-unknown-linux-gnu -disable-objc-interop -module-name main -o /tmp/28302-swift-paramdecl-createunboundself-53086d.o
1.	With parser at source location: validation-test/compiler_crashers/28302-swift-paramdecl-createunboundself.swift:11:1
<unknown>:0: error: unable to execute command: Aborted
<unknown>:0: error: compile command failed due to signal (use -v to see invocation)
```