Reduce the number of indirections in the attributes implementation.

- Coallocate entires for AttributeSetImpls and Nodes after the class itself.
- Remove mutable iterators from immutable classes.
- Remove unused context field from AttributeImpl.
- Derive Enum/Align/String attribute implementations from AttributeImpl instead
  of having a whole new inheritance tree for them.
- Derive AlignAttributeImpl from EnumAttributeImpl.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@186075 91177308-0d34-0410-b5e6-96231b3b80d8
Sync llvm-ar's help string with the options it supports.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@186076 91177308-0d34-0410-b5e6-96231b3b80d8
Remove support for truncating names in archives.

* All systems we support have some form of long name support.
* The options has different names and semantics in different implementations
  ('f' on gnu, 'T' on OS X), which makes it unlikely it is normally used on
  build systems.
* It was completely untested.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@186078 91177308-0d34-0410-b5e6-96231b3b80d8
Delete dead code.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@186079 91177308-0d34-0410-b5e6-96231b3b80d8