fine granular buildworld time statistic by stages and subdirs

For the `make buildworld' we log the time spent in each stage
(bootstrap tools, building libraries, everything etc), as documented
in
https://www.freebsd.org/status/report-2021-07-2021-09/#_current_compilation_time_analysis

It would be great if we have more fine granular statistics based on
the subdir targets. It turns out that is pretty easy with a wrapper
shell script.

apply the patch from https://reviews.freebsd.org/D50534
$ chmod 755 ./tools/build/time-buildworld*

build the world
$ make buildworld > buildworld.log

The generated CSV has ca. 2800 lines
$ ./tools/build/time-buildworld-csv.awk buildworld.log > buildworld.csv

output example:
https://people.freebsd.org/~wosch/build-time/buildworld/buildworld.csv
https://people.freebsd.org/~wosch/build-time/buildworld/buildworld.log.gz

The statistics will be generated as CSV, because this is a very simple
format and runs on a base system without ports installed.

Comments are welcome, Wolfram

-- 
Wolfram Schneider <wosch@FreeBSD.org> https://wolfram.schneider.org