DAG->DAG instruction selection for ia64! "hello world" works, not much else.

use -enable-ia64-dag-isel to turn this on

TODO: delete lowering stuff from the pattern isel
    : get operations on predicate bits working
    : get other bits of pseudocode going
    : use sampo's mulh/mull-using divide-by-constant magic
    : *so* many patterns ("extr", "tbit" and "dep" will be fun :)
    : add FP
    : add a JIT!
    : get it working 100%

in short: this'll be happier in a couple of weeks, but it's here now so
the tester can make me feel guilty sooner.

OTHER: there are a couple of fixes to the pattern isel, in particular
making the linker happy with big blobs of fun like pypy.

llvm-svn: 24058