SOLVED.
It's a bug in MariaDB.
https://mariadb.atlassian.net/browse/MDEV-6340?focusedCommentId=52089&pa...
It mainfests when GCC 4.9 is used.
The issue's ID'd at
"Operational Notification -- Changes in gcc Code Optimization Can Cause a Crash in BIND" https://kb.isc.org/article/AA-01167
The workaround is to add
"CFLAGS=-fno-delete-null-pointer-checks"
to gcc compile options
Here, with MariaDB 10.0.12 / ReleaseBuild built with GCC 4.9 + CFLAGS=-fno-delete-null-pointer-checks, drush site-install of Drupal 7.28 exec with no errors, and `drush *` works on existing site with no errors.