Update jobs.mk to leverage -jC

With bmake-20230909 we can use -j1.5C to use 1.5*ncpu
bmake will set .MAKE.JOBS.C=yes if this is supported,
and in that case jobs.mk will use JOB_MAX_C as default for JOB_MAX.

Remove logic from local.sys.mk which is now handled by jobs.mk

Also use latest dirdeps-targets.mk and meta.{autodep,subdir}.mk

jobs.mk report JOB_ARGS log and JOB_LOG_START

At the start of a job include info such as JOB_ARGS the log location
and anything in JOB_LOG_START (eg TARGET_SPEC=${TARGET_SPEC})

Add jobs.mk to allow for target-jobs

jobs.mk automates -j$JOB_MAX and capturing build log based on target.

Compute a default for JOB_MAX in local.sys.mk

Reviewed by: stevek, imp
Differential Revision: https://reviews.freebsd.org/D39683