#188400 regressed data-section folding under --icf=safe{,_thunks}:
no-addrsig fallback, and over-broad compiler-emitted addrsig entries
covering data symbols, both caused markSymAsAddrSig to set keepUnique on
data sections, after which foldIdenticalSections refused to fold them.
ld64 coalesces __cfstring, __objc_classrefs and __objc_selrefs
unconditionally regardless of addrsig, so ignore keepUnique for them as
a workaround for the imprecise addrsig payload.
Zhaoxuan Jiang
75fbd79163