[PATCH] [DWARF] Fix a few corner cases in expression emission

[Keno Fischer]

Is `DW_OP_reg5 DW_OP_plus_uconst 4` actually valid DWARF? My reading of the spec was that you had to express that as 
 `DW_OP_breg5 4 DW_OP_stack_value`, but of course I can't argue with a DWARF committee member ;).


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  rL LLVM

http://reviews.llvm.org/D10302

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