This patch applies upstream commit:
https://github.com/google/benchmark/commit/f0901417c89d123474e6b91365029cfe32cf89dc

Tim Northover pointed out that benchmark build might be broken on 32-bit
macOS. This commit by Roman Lebedev (lebedev.ri) resolves the issue.

Reviewed By: lebedev.ri

Differential Revision: https://reviews.llvm.org/D51677

llvm-svn: 341469