GHS-MULTI: Enable compiler with Ninja and Makefile generators

According to !3839 (comment 629414) it is possible to use these generators with the GHS compiler by always passing -bsp ... and -os_dir ... arguments. We have other platforms where we add necessary arguments to compilers automatically based on configurable settings rather than asking users to pass flags themselves. We should consider doing that for GHS-MULTI too.

It could be done in Modules/Platform/GHS-MULTI-GHS-{C,CXX}.cmake modules.

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