[SR-12193] The warning returned when SwiftPM couldn't find a dependency of a PC file is confusing

[hartbit]

Previous ID	SR-12193
Radar	rdar://problem/59496034
Original Reporter	@hartbit
Type	Task

Additional Detail from JIRA

Votes	0
Component/s	Package Manager
Labels	Task
Assignee	None
Priority	Medium

md5: 6a7169fef09e93ec7f98770bf3c7a786

Issue Description:

When SwiftPM fails to find the dependency of a PC file, it emits a warning that gives the impression it couldn't find the original PC file, not the dependency.

[beccadax]

@swift-ci create