Merging r310543:

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r310543 | pcc | 2017-08-09 18:07:44 -0700 (Wed, 09 Aug 2017) | 9 lines

Linker: Create a function declaration when moving a non-prevailing alias of function type.

We were previously creating a global variable of function type,
which is invalid IR. This issue was exposed by r304690, in which we
started asserting that global variables were of a valid type.

Fixes PR33462.

Differential Revision: https://reviews.llvm.org/D36438
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llvm-svn: 318181