Switch Alpha over to the new call lowering style. New code mostly

Switch Alpha over to the new call lowering style.  New code mostly
copied from the SystemZ target.  I don't think this causes any
significant changes to the output (I compared the assembly, and the
results appeared to be essentially unchanged), although I don't actually
have an Alpha to test on.

I would appreciate if anyone with the appropriate hardware could test
this. I'm not sure if that includes anyone subscribed to llvm-commits,
though.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@76353 91177308-0d34-0410-b5e6-96231b3b80d8