[MC][MCParser] Mark local and weak symbols as such when parsing assembly text

[sdardis]

Summary

When parsing assembly text directives such as .local, .weak, the symbols were
not marked as such in the internal symbol table. This lead to different output
depending on whether MCAsmStreamer or MCELFStreamer was. This patch
corrects such behaviour.

[sdardis]

dsanders observed this behaviour in D23497. I've since reposted that patch as D24722.

[sdardis]

Expanded MCSymbol<ELF/COFF/MachO> to dump internal state. Expanded MCContext to be able to dump the symbol table. Added a new hidden option -asm-show-symbol-table that prints out the symbol table just before the AsmParser finishes running.

[vkalintiris]

We should split this in two separate review requests, ie. one that introduces symbol dumping and another that marks local and weak symbols. Can you also add a separate test file just for checking the newly introduced -asm-show-symbol-table option?

lib/MC/MCParser/ELFAsmParser.cpp

if (getLexer().isNot(AsmToken::EndOfStatement)) {
     for (;;) {
       StringRef Name;
 
       if (getParser().parseIdentifier(Name))
         return TokError("expected identifier in directive");
 
       MCSymbol *Sym = getContext().getOrCreateSymbol(Name);
 
+      if (Attr == MCSA_Local) {
+        cast<MCSymbolELF>(Sym)->setBinding(ELF::STB_LOCAL);
+      } else if (Attr == MCSA_Weak) {
+        cast<MCSymbolELF>(Sym)->setBinding(ELF::STB_WEAK);
+      }
+
       getStreamer().EmitSymbolAttribute(Sym, Attr);
 
       if (getLexer().is(AsmToken::EndOfStatement))
         break;
 
       if (getLexer().isNot(AsmToken::Comma))
         return TokError("unexpected token in directive");
       Lex();