Well, to be honest, I have know idea where this is set per default. Check in your ndk root directory. There is a ndk.sh/bat file (or similar) which sets all those envs.
You start the Momentics IDE with a batch file. In that batch file you can set a couple of things for the shell Momentics is started within. So, I guess it would be possible to set it there. But, depending on the version of Momentics you start (you would need to start the one from the BB NDK 2.0) this is set in the settings for the "C/C++ Build"/"Project Properties" menu. There you usually select the ARM or x86 compiler which specifies this very line to define chose which compiler to compile your code with.
Not sure how the QNX plugin is configured with this exact command line. I'd say this is hardcoded (??) in the resp. QNX plugin within the resp ndk (2.0 or 10). I don't think there is an option in Momentics where you can actually configure the compiler version you want to use. This is probably part of the BB plugin. I'll have to look it up. I am just trying to remember out of my head here.
BTW: This is if you want to compile with the BB NDK 2.0. If you go the other way round your HOST/TARGET needs to be adjusted to the BB 10 NDK (root directory is wrong in that error message of yours). Then you start Momentics from there and your code should compile. Not sure if this will run on the Playbook - asuming you are not using any BB10 features explicitly...?
