Merging r339217:
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r339217 | cdavis | 2018-08-08 06:21:24 +0200 (Wed, 08 Aug 2018) | 11 lines

[libunwind] Fix pointer-to-integer cast warnings on LLP64.

Summary:
`long` is too short on LLP64. We have to use `intptr_t` to
avoid truncating pointers.

Reviewers: mstorsjo, rnk, compnerd, smeenai

Subscribers: christof, cfe-commits, llvm-commits

Differential Revision: https://reviews.llvm.org/D50412
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git-svn-id: https://llvm.org/svn/llvm-project/libunwind/branches/release_70@339222 91177308-0d34-0410-b5e6-96231b3b80d8