zos: set compiler flags based on compiler and node versions
zos: set compiler flags based on compiler and node versions

This is to workaround previous (to v14) versions of node
and a compiler bug affected by those versions, as follows:

- v8 (ships with D190508), requires -U_VARARG_EXT_ and no-opt
- v12 (ships with D191122), requires no-opt
- v14 (ships with D191122), no workaround needed.

joeferner/node-java,joeferner/node-java,joeferner/node-java,joeferner/node-java,joeferner/node-java,joeferner/node-java