[lld][test] Precommit test for ld -r links with FatLTO PIC objects (#92817)

Currently, with PIC relocatable links, FatLTO sections are treated as
orphan
sections and incorrectly concatenated together. This test verifies the
current
behavior, but should be fixed to either merge those sections into a
single llvm
module, similar to what `llvm-link` would produce, or to drop them
altogether.