dtrace: Add WITH_DTRACE_ASAN

This option is a blanket for all the DTrace-related software. The option
when enabled passes in -fsanitize=address -fsanitize=undeifned, enabling
ASAN and UBSAN in the following components:

• libdtrace
• dtrace(1)
• lockstat(1)
• plockstat(1)

The option defaults to "no" and is intended as a developer aid.

Reviewed by: markj
Differential Revision: https://reviews.freebsd.org/D41157