[lld-macho] Read in new addrsig format

[int3]

Summary

The new format uses symbol relocations, as described in D127637: [MC][MachO] Change addrsig format + ensure its size is properly set.

[alx32]

Looks good !

lld/MachO/ICF.cpp

for (InputFile *file : inputFiles) {
     if (!obj)
       continue;
 
     Section *addrSigSection = obj->addrSigSection;
     if (!addrSigSection)
       continue;
     assert(addrSigSection->subsections.size() == 1);
 
-    Subsection *subSection = &addrSigSection->subsections[0];
-    ArrayRef<unsigned char> &contents = subSection->isec->data;
+    const InputSection *isec = addrSigSection->subsections[0].isec;
 
-    const uint8_t *pData = contents.begin();
-    while (pData != contents.end()) {
-      unsigned size;
-      const char *err;
-      uint32_t symIndex = decodeULEB128(pData, &size, contents.end(), &err);
-      if (err)
-        fatal(toString(file) + ": could not decode addrsig section: " + err);
-      markSymAsAddrSig(obj->symbols[symIndex]);
-      pData += size;
+    for (const Reloc &r : isec->relocs) {
+      if (auto *sym = r.referent.dyn_cast<Symbol *>())
+        markSymAsAddrSig(sym);
+      else
+        error(toString(isec) + ": unexpected section relocation");
     }
   }
 }
 
 void macho::foldIdenticalSections() {
   TimeTraceScope timeScope("Fold Identical Code Sections");
   // The ICF equivalence-class segregation algorithm relies on pre-computed
   // hashes of InputSection::data for the ConcatOutputSection::inputs and all