[CodeExtractor] Use subset of function attributes for extracted function.

In addition to target-dependent attributes, we can also preserve a
white-listed subset of target independent function attributes. The white-list
excludes problematic attributes, most prominently:

* attributes related to memory accesses, as alloca instructions
  could be moved in/out of the extracted block

* control-flow dependent attributes, like no_return or thunk, as the
  relerelevant instructions might or might not get extracted.

Thanks @efriedma and @aemerson for providing a set of attributes that cannot be
propagated.


Reviewers: efriedma, davidxl, davide, silvas

Reviewed By: efriedma

Differential Revision: https://reviews.llvm.org/D41334

llvm-svn: 321961

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