Unified Build behavior control update for emsdk

[mmitche]

I couldn't figure out the best area label to add to this issue. If you have write-permissions please help me learn by adding exactly one area label.

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Issue Details

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Author:	mmitche
Assignees:	-
Labels:	untriaged, area-Infrastructure-mono, needs-area-label
Milestone:	-

[mmitche]

Emsdk appears to have no existing usages of DotNetBuildFromSource. Closing.