This enhances the macro parser to parse and handle parameter qualifications,
which is needed to support required formal parameters in macro definitions. A
required parameter may not be defaulted (though providing a default value is
accepted with a warning). This improves GAS compatibility.
Partially addresses PR9248.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@201630 91177308-0d34-0410-b5e6-96231b3b80d8
