ELF: Parse types in directives like binutils gas

Allow binutils .type and .section directives to take the following
forms:
- @<type>
- %<type>
- "<type>"


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@191134 91177308-0d34-0410-b5e6-96231b3b80d8