Add a few more c'tors:

Add a few more c'tors:

* One that accepts a single Attribute::AttrKind.

* One that accepts an Attribute::AttrKind plus a list of values. This is for
  attributes defined like this:

    #1 = attributes { align = 4 }

* One that accepts a string, for target-specific attributes like this:

    #2 = attributes { "cpu=cortex-a8" }

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@171249 91177308-0d34-0410-b5e6-96231b3b80d8