Reland r298901 with modifications (reverted in r298932)

Dont emit Mapping symbols for sections that contain only data.

Summary:
Dont emit mapping symbols for sections that contain only data.

Reviewers: rengolin, weimingz, kparzysz, t.p.northover, peter.smith

Reviewed By: t.p.northover

Patched by Shankar Easwaran <shankare@codeaurora.org>

Subscribers: alekseyshl, t.p.northover, llvm-commits

Differential Revision: https://reviews.llvm.org/D30724

llvm-svn: 299392