build: Correctly check for Python modules

Currently using Meson the command "python -m <MODULE_NAME>" is run. However this command instead of trying to import the module tried to execute it as a script failing for the updated pyparsing with:

/usr/bin/python3: No module named pyparsing.__main__; 'pyparsing' is a package and cannot be directly executed

So instead use "python -c 'import <MODULE_NAME>". Autoconf is already using that command (see m4/ax_python_module.m4).

Signed-off-by: Frediano Ziglio freddy77@gmail.com