#define constants are missing from the completion list

[potterdai]

Environment data

dotnet --info output:
VS Code version: 1.7.2
C# Extension version:
1.5.3

Steps to reproduce

Using DefineConstants within the project.

Expected behavior

All DefineConstants should be under intellisense.

Actual behavior

None DefineConstants appears in intellisense.

[DustinCampbell]

This should ultimately be addressed by OmniSharp/omnisharp-roslyn#78.