Besides fixing output capture, it also fixes a strange bug in MSBuild
where if the command list is too long, it will remove random
characters from the command list before passing it to the command.
Closes https://github.com/mesonbuild/meson/issues/1417
For commands that always output to stdout and don't have a "-o" or
"--output" or some other similar option, this 'capture' setting allows
the build to capture the result and place it in the output file.