Switch all DWARF variables for tags, attributes and forms over to use the llvm::dwarf...

Switch all DWARF variables for tags, attributes and forms over to use the llvm::dwarf enumerations instead of using raw uint16_t values. This allows easier debugging as users can see the values of the enumerations in the variables view that will show the enumeration string instead of just a number.

https://reviews.llvm.org/D26013

llvm-svn: 285309