This issue was discussed in https://forums.swift.org/t/linker-error-on-ubuntu-18-04-swift-5-1-2/31168.
When building a "large" Swift project on Linux such as https://github.com/finlabsuk/open-banking-connector it seems the following error is produced on linking:
The issue is reproducible with the above-mentioned project on Swift 5.1.2 / Ubuntu 18.04 (build instructions here: https://github.com/finlabsuk/open-banking-connector/blob/master/docs/installation-and-use.md).
Analysis (https://forums.swift.org/t/linker-error-on-ubuntu-18-04-swift-5-1-2/31168/8) suggests the cause is related to the compiler producing a high number of output files per input files which might be reducible. In any case an actionable error message would be helpful as this situation seems to arise quite easily.