Fix various compiler/linker warnings when building with link time optimization:
 [-Werror=free-nonheap-object]
 [-Werror=maybe-uninitialized]
 [-Werror=stringop-truncation]

Downgrade -Werror=odr to warning for mysqld and unit test executables
which link in the entire server. We know we have ODR violations due to
multiple bison parsers.

Downgrade -Werror=stringop-truncation for 3rd party code.

Change-Id: Id5f733028b378df7cd89ec2d17e52d038d8e664b