FR: add SQLCHECK option to gixsql

[GitMensch]

See Oracle Pro*COB docs "Syntactic and Semantic Checking" to prevent bad SQL (type mismatch) or non-existing tables/columns/typos to only happen at runtime.

Additional this may allow to provide an option to do parts of the currently dynamic parts happen already at compile time (setup of DB types/lengths/...) speeding up the actual access.