This is the actual compiler error. The landmass log notice is just a notice about what it’s building.
The real problem is the Runtime\Core\Public\Experimental\ConcurrentLinearlAllocator.h header.
Are you sure landmass is the only plugin or only C++ code you’re using? It might be something else including the experimental header.
Also note the compiler version warning:
First, fix the compiler version, and re-generate your projects and re-build.
If that doesn’t work, figure out what it is that includes this experimental header, and if it’s not Landmass, address that.
If neither of these solve the problem, you might want to temporarily define that missing macro by making some local edits.