Change how SkDebugf is sent to stdout on Android.

Previously, a function was called using dlsym in skia_launcher.

Add a static initializer that changes the setting, and include that for
the tools we automate for testing.

Also only do va_copy if we actually use it.

BUG=skia:2454

Review URL: https://codereview.chromium.org/753543003
5 files changed