Copy stable/9 to releng/9.3 as part of the 9.3-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

MFC r252325:
The dtmalloc provider uses the short description of a malloc type as the
function name of its corresponding DTrace probes. These descriptions may
contain whitespace, but probe names cannot, so just replace any whitespace
with underscores when creating probes.

Copy head to stable/9 as part of 9.0-RELEASE release cycle.

Approved by: re (implicit)

Custom DTrace kernel module files plus FreeBSD-specific DTrace providers.