dtrace: Add WITH_DTRACE_ASAN

See commit 4ae6991228105eb34989c870194ae7b0a1e23be4. This version of
the commit avoids inadvertently changing SHLIBDIR for libdtrace.so.

dtrace: Revert the addition of WITH_DTRACE_ASAN

The follow-up fix triggers a lib32 build failure, revert everything
until the problem is addressed.

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