Merging r366504:

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r366504 | tlively | 2019-07-18 23:50:24 +0200 (Thu, 18 Jul 2019) | 15 lines

[WebAssembly] Use passive segments by default when memory is shared

Summary:
This change makes it so that passing --shared-memory is all a user
needs to do to get proper multithreaded code. This default can still
be explicitly overridden for any reason using --passive-segments and
--active-segments.

Reviewers: sbc100, quantum

Subscribers: dschuff, jgravelle-google, aheejin, sunfish, jfb, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D64950
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llvm-svn: 366709