Now that we have everything nicely factored (e.g. asmprinter is not

Now that we have everything nicely factored (e.g. asmprinter is not
doing global variable classification anymore) and hookized, sink almost
all target targets global variable emission code into AsmPrinter and out
of each target.

Some notes:

1. PIC16 does completely custom and crazy stuff, so it is not changed.
2. XCore has some custom handling for extra directives.  I'll look at it next.
3. This switches linux/ppc to use .globl instead of .global.  If .globl is
   actually wrong, let me know and I'll fix it.
4. This makes linux/ppc get a lot of random cases right which were obviously
   wrong before, it is probably now a bit healthier.
5. Blackfin will probably start getting .comm and other things that it didn't
   before.  If this is undesirable, it should explicitly opt out of these
   things by clearing the relevant fields of MCAsmInfo.

This leads to a nice diffstat:
 14 files changed, 127 insertions(+), 830 deletions(-)

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@93858 91177308-0d34-0410-b5e6-96231b3b80d8