[docs] Convert remaining command guide entries from md to rst.

Summary:
Linking between markdown and rst files is currently not supported very well, e.g. the current llvm-addr2line docs [1] link to "llvm-symbolizer" instead of "llvm-symbolizer.html". This is weirdly broken in different ways depending on which versions of sphinx and recommonmark are being used, so workaround the bug by using rst everywhere.

[1] http://llvm.org/docs/CommandGuide/llvm-addr2line.html

Reviewers: jhenderson

Reviewed By: jhenderson

Subscribers: lebedev.ri, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D66305

llvm-svn: 369553