Common symbol in executable is a definition, which overrides definition
from shared objects. When linker sees a new definition from a shared
object, the new dynamic definition should be overridden by the previous
common symbol in executable.
bfd/
PR ld/19579
* elflink.c (_bfd_elf_merge_symbol): Treat common symbol in
executable as definition if the new definition comes from a
shared library.
ld/
PR ld/19579
* testsuite/ld-elf/pr19579a.c: New file.
* testsuite/ld-elf/pr19579b.c: Likewise.
* testsuite/ld-elf/shared.exp: Run PR ld/19579 test.
