Crash when parsing a shader with a bitfield #1693

// dxc (bc9ad948) /T cs_6_0 shader.hlsl
struct Foo
{
	uint a : 1;
	uint b : 31;
};

//ConstantBuffer<Foo> Input;
StructuredBuffer<Foo> Input;
RWBuffer<uint> Output;

[numthreads(1,1,1)]
void main()
{
	Output[0] = Input[0].a;
}

[0x0]   VCRUNTIME140D!MoveSmall + 0x6b   
[0x1]   dxcompiler!std::char_traits<char>::move + 0x3c   
[0x2]   dxcompiler!std::basic_string<char,std::char_traits<char>,std::allocator<char> >::assign + 0x78   
[0x3]   dxcompiler!std::basic_string<char,std::char_traits<char>,std::allocator<char> >::operator= + 0x8a   
[0x4]   dxcompiler!hlsl::DxilFieldAnnotation::SetFieldName + 0x39   
[0x5]   dxcompiler!`anonymous namespace'::CGMSHLSLRuntime::ConstructStructAnnotation + 0x73b   
[0x6]   dxcompiler!`anonymous namespace'::CGMSHLSLRuntime::AddTypeAnnotation + 0x372   
[0x7]   dxcompiler!`anonymous namespace'::CGMSHLSLRuntime::ConstructStructAnnotation + 0x646   
[0x8]   dxcompiler!`anonymous namespace'::CGMSHLSLRuntime::AddTypeAnnotation + 0x465   
[0x9]   dxcompiler!`anonymous namespace'::CGMSHLSLRuntime::SetUAVSRV + 0x1c7   
[0xa]   dxcompiler!`anonymous namespace'::CGMSHLSLRuntime::AddUAVSRV + 0x548   
[0xb]   dxcompiler!`anonymous namespace'::CGMSHLSLRuntime::addResource + 0x24a   
[0xc]   dxcompiler!clang::CodeGen::CodeGenModule::EmitTopLevelDecl + 0x1a8   
[0xd]   dxcompiler!`anonymous namespace'::CodeGeneratorImpl::HandleTopLevelDecl + 0xb5   
[0xe]   dxcompiler!clang::BackendConsumer::HandleTopLevelDecl + 0xf8   
[0xf]   dxcompiler!clang::ParseAST + 0x284   
[0x10]   dxcompiler!clang::ASTFrontendAction::ExecuteAction + 0x12b   
[0x11]   dxcompiler!clang::CodeGenAction::ExecuteAction + 0x69d   
[0x12]   dxcompiler!clang::FrontendAction::Execute + 0x8c   
[0x13]   dxcompiler!DxcCompiler::CompileWithDebug + 0x1475   
[0x14]   dxcompiler!DxcCompiler::Compile + 0xc7   
[0x15]   dxc!DxcContext::Compile + 0xcd3