"make --help" needs to show test targets

[tbrowder]

After building and installing rakudo, the resulting Makefile does not show the available "make" test targets (e.g., "make spectest"). Currently -"make --help" shows:

Usage: make [options] [target] ...
Options:
 -b, -m                      Ignored for compatibility.
 -B, --always-make           Unconditionally make all targets.
 -C DIRECTORY, --directory=DIRECTORY
                             Change to DIRECTORY before doing anything.
 -d                          Print lots of debugging information.
 --debug[=FLAGS]             Print various types of debugging information.
 -e, --environment-overrides
                             Environment variables override makefiles.
 --eval=STRING               Evaluate STRING as a makefile statement.
 -f FILE, --file=FILE, --makefile=FILE
                             Read FILE as a makefile.
 -h, --help                  Print this message and exit.
 -i, --ignore-errors         Ignore errors from recipes.
 -I DIRECTORY, --include-dir=DIRECTORY
                             Search DIRECTORY for included makefiles.
 -j [N], --jobs[=N]          Allow N jobs at once; infinite jobs with no arg.
 -k, --keep-going            Keep going when some targets can't be made.
 -l [N], --load-average[=N], --max-load[=N]
                             Don't start multiple jobs unless load is below N.
 -L, --check-symlink-times   Use the latest mtime between symlinks and target.
 -n, --just-print, --dry-run, --recon
                             Don't actually run any recipe; just print them.
 -o FILE, --old-file=FILE, --assume-old=FILE
                             Consider FILE to be very old and don't remake it.
 -O[TYPE], --output-sync[=TYPE]
                             Synchronize output of parallel jobs by TYPE.
 -p, --print-data-base       Print make's internal database.
 -q, --question              Run no recipe; exit status says if up to date.
 -r, --no-builtin-rules      Disable the built-in implicit rules.
 -R, --no-builtin-variables  Disable the built-in variable settings.
 -s, --silent, --quiet       Don't echo recipes.
 -S, --no-keep-going, --stop
                             Turns off -k.
 -t, --touch                 Touch targets instead of remaking them.
 --trace                     Print tracing information.
 -v, --version               Print the version number of make and exit.
 -w, --print-directory       Print the current directory.
 --no-print-directory        Turn off -w, even if it was turned on implicitly.
 -W FILE, --what-if=FILE, --new-file=FILE, --assume-new=FILE
                             Consider FILE to be infinitely new.
 --warn-undefined-variables  Warn when an undefined variable is referenced.

This program built for x86_64-pc-linux-gnu
Report bugs to <bug-make@gnu.org>

[coke]

Right, make help is helping with make in general, not our specific build targets. I don't think there's a standard for this.

Here's a SF overflow page on how to show makefile targets:

https://stackoverflow.com/questions/4219255/how-do-you-get-the-list-of-targets-in-a-makefile

There are notes in INSTALL.md, which I have found to be a standard place to find build/install instructions.