message: Allow bool

[xclaesse]

It has always been working even if not documented and there is no reason
to not accept it. However, change "True/False" to "true/false" to be
consistent with meson language.

Fixes: #9436

[eli-schwartz]

TBH I don't even understand the point of writing Message: true to the console. What are people using this for? Is there a better way?

[xclaesse]

Certainly something like: message('the value of option foo is', get_option('foo')) for a boolean option.

[dcbaker]

I assume printf debugging

[codecov]

Codecov Report

Merging #9447 (6a5daa8) into master (954fa95) will decrease coverage by 3.15%.
The diff coverage is n/a.

❗ Current head 6a5daa8 differs from pull request most recent head 5dff016. Consider uploading reports for the commit 5dff016 to get more accurate results

@@            Coverage Diff             @@
##           master    #9447      +/-   ##
==========================================
- Coverage   67.31%   64.16%   -3.16%     
==========================================
  Files         396      198     -198     
  Lines       85440    42685   -42755     
  Branches    17655     8735    -8920     
==========================================
- Hits        57518    27390   -30128     
+ Misses      23237    12999   -10238     
+ Partials     4685     2296    -2389     

Impacted Files	Coverage Δ
envconfig.py	73.20% <0.00%> (-0.89%)	⬇️
mcompile.py	53.19% <0.00%> (-0.50%)	⬇️
compilers/detect.py	41.85% <0.00%> (-0.18%)	⬇️
mesonbuild/mcompile.py
mesonbuild/envconfig.py
mesonbuild/interpreter/interpreter.py
mesonbuild/compilers/detect.py
mesonbuild/dependencies/coarrays.py
mesonbuild/templates/sampleimpl.py
mesonbuild/scripts/depscan.py
... and 191 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 6ea4e21...5dff016. Read the comment docs.

[eli-schwartz]

As long as this is actually documented (and we print something that is actually consistent) which it now is, LGTM.