[ThinLTO] Rework llvm-link to use the FunctionImporter

Summary:
Change llvm-link to use the FunctionImporter handling, instead of
manually invoking the Linker. We still need to load the module
in llvm-link to do the desired testing for invalid import requests
(weak functions), and to get the GUID (in case the function is local).

Also change the drop-debug-info test to use llvm-link so that importing
is forced (in order to test debug info handling) and independent of
import logic changes.

Reviewers: mehdi_amini

Subscribers: mgorny, llvm-commits, aprantl

Differential Revision: https://reviews.llvm.org/D28277

llvm-svn: 290964

0 files changed, 0 insertions, 0 deletions