[ELF] - Fixed assertion fail when symbol table has invalid sh_info value.

[grimar]

Summary

This part was splitted from D25016.

When sh_info value was set in the way that non-local symbol was treated as local, lld
was asserting, patch fixes that.

[ruiu]

LGTM

ELF/Writer.cpp

368

getFilename(F) + ": broken input file: getLocalSymbols returns a non-local symbol."

[grimar]

ELF/Writer.cpp

368

changed to "broken object" because "broken input file" makes this fatal to be 3 lines after formatting.

[grimar]

r283859

ELF/Writer.cpp

 // Local symbols are not in the linker's symbol table. This function scans
 // each object file's symbol table to copy local symbols to the output.
 template <class ELFT> void Writer<ELFT>::copyLocalSymbols() {
   if (!Out<ELFT>::SymTab)
     return;
   for (elf::ObjectFile<ELFT> *F : Symtab<ELFT>::X->getObjectFiles()) {
     StringRef StrTab = F->getStringTable();
     for (SymbolBody *B : F->getLocalSymbols()) {
+      if (!B->IsLocal)
+        fatal(getFilename(F) + ": invalid sh_info in symbol table");
       auto *DR = dyn_cast<DefinedRegular<ELFT>>(B);
       // No reason to keep local undefined symbol in symtab.
       if (!DR)
         continue;
       if (!includeInSymtab<ELFT>(*B))
         continue;
       if (B->getNameOffset() >= StrTab.size())
         fatal(getFilename(F) + ": invalid symbol name offset");

test/ELF/invalid/symtab-sh-info.s

 ## sh_info contains zero value. First entry in a symbol table is always completely zeroed,
 ## so sh_info should be at least 1 in a valid ELF.
 # RUN: not ld.lld %p/Inputs/symtab-sh_info2.elf -o %t2 2>&1 | FileCheck %s
 # CHECK: invalid sh_info in symbol table
+
+## sh_info contains invalid value saying non-local symbol is local.
+# RUN: not ld.lld %p/Inputs/symtab-sh_info3.elf -o %t2 2>&1 | \
+# RUN:   FileCheck --check-prefix=INVALID-SYMTAB-SHINFO %s
+# INVALID-SYMTAB-SHINFO: invalid sh_info in symbol table