Send trace logs to stderr instead of stdout

Stdout gets redirected to a makefile that is
ingested by the rest of the build system.
The trace outputs were being mixed up with
the rest of the output, making them hard to
read. In addition, some of the trace output
wasn't commented out, so it was defining
make rules.

Fixes: 230495885
Test: Manually
Change-Id: I02f9038cd89598fc1c1561bf4bf2997ac090d9e9