GUI build script on linux and osx assumes non default layout of opensim-core

[aymanhab]

Need to set OPENSIM_INSTALL_UNIX_FHS=OFF in opensim-core build to have GUI build successfully for now. Need to make the process more robust for the long term by either changing CMake defaults in opensim-core, change build.xml or at minimum check the flags used to build opensim-core.

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Expected result

Actual result

(include screen grabs where appropriate)

Environment and GUI version

[marnunez]

Could this be set as a CMake flag for the GUI? Say, just like the core is build for "Release" and afterwards one expects the GUI to be built for "Release", just add the remainder to build both "for FHS" and have the build.xml change accordingly?