GHS: changing os_dir to MACRO and fix -os_dir flag in gpj

Prior to the changes, /usr/ghs/installed_version_of_INTEGRITY was added to the generated gpj which is not an accepted statement in the gpj file, resulting in generating unusable project files. (should instead be the value provided by the flag -os_dir) The way that MULTI's new project wizard creats gpjs is that OS_DIR gets defined by a macro in the top-level GPJ, and the flag -os_dir is set to the macro. After the changes, the generated file is closer to what users familiar with MULTI expect, and projects targeting INTEGRITY can successfully generate.

Fixes: #25647 (closed)
Topic-rename: ghs-gpj-os_dir