Clarify cbuild schema check flag --schema

[ReinhardKeil]

Describe the bug

When cbuild is called with option --schema, on Windows the xmllint tool is required. Do we really need to check the XML input files? I believe the schema check should be limited to the YML input files.

Could you clearify what schema check is really enabled by this command? Is the csolution schema check disabled when this option is not used (csolution called with --no-check-schema)?

[jkrech]

Currently YML and XML schema checks are unified, it's enabled or disabled for both (disabled by default).

When the cbuild tool runs with yml as input, there is no need to check the XML (cprj) schema as cprj is generated by the csolution tool.
Only when the cbuild tool command is buildcprj and therefore the input file must be a *.cprj file (cbuild buildcprj myproject.cprj) the --schema flag should invoke the xmllint tool on the specified *.cprj file.