LTO may optimize out a plugin symbol, which is also referenced by a
non-IR file. When that happens, we should mark the plugin symbol
undefined. It isn't the problem since LTO already determined the
symbols in the non-IR file aren't used.
bfd/
PR ld/12365
PR ld/14272
* elflink.c (_bfd_elf_fix_symbol_flags): Mark the plugin symbol
undefined if it is referenced from a non-IR file.
ld/testsuite/
PR ld/12365
* ld-plugin/pr12365a.c: New file.
* ld-plugin/pr12365b.c: Likewise.
* ld-plugin/pr12365c.c: Likewise.
* ld-plugin/lto.exp (lto_link_tests): Prepare for the PR ld/12365
test.
Run the PR ld/12365 test.
