Zygote: Set libbase default tag on fork

When forking, set the default tag to the process name, so that
non-tagged logging (like ART's) get tagged accordingly.

(cherry picked from commit 39613974)

Bug: 34867873
Test: m
Merged-In: I81d526c8f5af0fde488cdf8efd1835298ff501fc
Change-Id: I81d526c8f5af0fde488cdf8efd1835298ff501fc