Backport ARM ELF Streamer and unwind opcode assembler.

The initial effort to support -integrate-as.  This includes
several commits from upstream (listed below), and some
modification to fit LLVM 3.2.

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svn rev  git sha1
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r181603  81c74e94f71ec1a7e09b9705d4f3cca437ece971
r179591  532854d7
r174372  b0c89966
r173939  52b1b3bb
r169965  37c7461f
r169603  64501653
r167945  062a6c83
r167904  25efd6d5
r167633  12cfa119
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Change-Id: I59a433dd6012ef0c475a846f5eb157b315d326de