[Object] Also treat STB_GNU_UNIQUE symbols as exported to other DSO

All of STB_GLOBAL/STB_WEAK/STB_GNU_UNIQUE are treated as export symbols, see:

glibc/elf/dl-lookup.c:do_lookup_x
musl/ldso/dynlink.c OK_BINDS

Though ld.so does not read binding, the currently used STV_DEFAULT or STV_PROTECTED is a good emulation of linker behavior.

llvm-svn: 347481