OS X's ar(1) doesn't allow us to create an archive with no object files.
This patch adds a stub file with a stub function in it to make OS X
happy again.
This commit adds the src/trace directory containing the basics for our tracing
subsystem. It is not used in the code base. The "src/trace/debug.h" file
contains an example on how we can map our tor trace events to log_debug().
The tracing subsystem can only be enabled by tracing framework at compile
time. This commit introduces the "--enable-tracing-debug" option that will
make all "tor_trace()" function be maped to "log_debug()".
Closes#13802
Signed-off-by: David Goulet <dgoulet@torproject.org>
