go/ssa: add associated documentation to functions

[aykevl]

This makes it easier for clients to read compiler directives like //go:linkname or //line.

I would like to use this in my own Go compiler project.

[gopherbot]

Message from Gerrit User 5976:

Patch Set 1:

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[gopherbot]

Message from Gerrit User 5195:

Patch Set 1:

(1 comment)

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[gopherbot]

Message from Gerrit User 5020:

Patch Set 1:

(1 comment)

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[gopherbot]

Message from Gerrit User 5195:

Patch Set 1:

(1 comment)

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[gopherbot]

Message from Alan Donovan:

Patch Set 1: Code-Review-1

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[gopherbot]

Message from Ayke van Laethem:

Patch Set 1:

Oops, I forgot about this change. I have used you

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[gopherbot]

Message from Ayke van Laethem:

Patch Set 1:

Patch Set 1:

Oops, I forgot about this change. I have used you

*I have used your change and it has worked well for me. (Hit the wrong button).

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