Add support for NoDebugAttr

[cornelk]

Fixes panic: unknown node type: 'NoDebugAttr 0x2ebd788 <col:59>'

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This change is 

[elliotchance]

Reviewed 5 of 5 files at r1.
Reviewable status: complete! all files reviewed, all discussions resolved

[elliotchance]

This PR is fine, but there are build failures unrelated to the change because it looks like travis has changed their underlying image. As to not break dev, I will put in a PR to update the build first.

Reviewable status: complete! all files reviewed, all discussions resolved

[elliotchance]

I have tried to update go and clang. However, there are a few years of upgrades and the changes are not trivial: #828

The next few months will be too busy for me to visit this project in any more depth. You are welcome to try and get the build working with my changes and I will happily review and merge it.

Unfortunately this means this PR will remain stalled until then.

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (master@4de3ec9). Click here to learn what that means.
Patch coverage: 52.38% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff            @@
##             master     #827   +/-   ##
=========================================
  Coverage          ?   77.86%           
=========================================
  Files             ?      170           
  Lines             ?     9814           
  Branches          ?        0           
=========================================
  Hits              ?     7642           
  Misses            ?     1695           
  Partials          ?      477           

Impacted Files	Coverage Δ
ast/position.go	76.82% <0.00%> (ø)
ast/no_debug_attr.go	52.94% <52.94%> (ø)
ast/ast.go	98.35% <100.00%> (ø)

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