Error compiling r494 with Linux Mint 18

Hello, I'm having difficulties compiling r494 with Linux Mint 18/GCC6. I've tried GCC4.6 and GCC5 as well, with similar unsuccessful results. I've pasted the relevant bits from the compile below. Bart, can you (or anyone) help please?
Thanks...
Thanks...
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Logger.o obj/Format.o -o bin/Supermodel `sdl-config --libs` -lGL -lGLU -lz -lm -lstdc++
obj/New3D.o: In function `New3D::CNew3D::~CNew3D()':
New3D.cpp:(.text+0x160): undefined reference to `New3D::R3DScrollFog::~R3DScrollFog()'
obj/New3D.o: In function `New3D::CNew3D::CNew3D()':
New3D.cpp:(.text+0x249b): undefined reference to `New3D::R3DScrollFog::R3DScrollFog()'
obj/New3D.o: In function `New3D::CNew3D::RenderFrame()':
New3D.cpp:(.text+0x5bf8): undefined reference to `New3D::R3DScrollFog::DrawScrollFog(float, float, float, float)'
obj/New3D.o: In function `New3D::CNew3D::DrawScrollFog()':
New3D.cpp:(.text+0x8a0): undefined reference to `New3D::R3DScrollFog::DrawScrollFog(float, float, float, float)'
collect2: error: ld returned 1 exit status
Makefile:129: recipe for target 'all' failed
make: *** [all] Error 1