Make the stdatomic shim and mutexatomic type complete

Mark Andrews requested to merge ondrej/add-16-bit-stdatomic-shims-v9_16 into v9_16

The stdatomic shims for non-C11 compilers (Windows, old gcc, ...) and mutexatomic implemented only and minimal subset of the atomic types. This commit adds 16-bit operations for Windows and all atomic types as defined in standard.

(cherry picked from commit bccea586)

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