cosmogatokat, you didn't got it:
- Haiku gcc2h (the official supported version) comes with 2 arch: x86_gcc2 and x86_gcc5
- Blender will never run on gcc2h haiku as primary arch, but there is a chance that it could be built on secondary arch (as it compiles on x86_64 just fine and gcc2h got the same compiler as secondary arch)
- You trying to build it hovewer for primary arch ( haikuporter blender-2.78a --get-dependencies <- see, no x86 in your command so haikuporter will try build for primary arch)
- There is no libgomp for gcc2 primary arch AFAIK
So, please, do a favor:
Remove the second ! from this line:
ARCHITECTURES="!x86_gcc2 !x86 x86_64"
(you can remove the first one too, but it won't change the fact, that blender will NEVER EVER work on gcc2h primary arch. It is written in stone.)
And run haikuporter as:
haikuporter blender_x86 --get-dependencies
It MUST be _x86, because it tells to HaikuPorter, that the target arch is the secondary arch, and it needs the get-dependencies, because you do not want to build everything, just blender.
Hope it helps.
If it isn't clear, please invest some time to understand the concept, the haikuporter wiki explains everything and the guys and girls at the Haiku IRC are really nice and helpful.