Summary:
Lookup and subsequent insert was done using uninitialized
FileSpec object, which caused the cache to be a no-op.
Bug: llvm.org/PR45310
Depends on D76804.
Reviewers: labath, JDevlieghere
Reviewed By: labath
Subscribers: mgorny, jingham, lldb-commits
Tags: #lldb
Differential Revision: https://reviews.llvm.org/D76805