Remove some c_str() calls.

Use the clang RemoveCStrCalls tool to automatically migrate the
code. This was only run on linux, so does not have any positive or
negative effect on other platforms.
Remove c_str calls when using stream APIs.

Use an ad-hoc clang tool for matching the calls which should be
ported.
Merge topic 'remove-c_str-calls' into next

af8a1643 Remove c_str calls when using stream APIs.
21c573f6 Remove some c_str() calls.