Fix warnings preventing copy elision.

Summary:
Moving a temporary object prevents copy elision, which is exactly
what clang points out by warning about this pattern.

The fix is simply removal of std::move applied to temporary objects.

Reviewers: clayborg

Subscribers: lldb-commits

Differential Revision: https://reviews.llvm.org/D23825
Author: Taras Tsugrii <ttsugrii@fb.com>

llvm-svn: 279724