Build fails on aarch64 Manjaro Linux (arch)

Hello,

Using Manjaro (arch) Linux aarch64
cmake 3.16.2
gcc 9.2.0
make 4.2.1

after running the included build_deps.sh and successful cmake . I get the following error

Scanning dependencies of target 3D_LIB
[ 82%] Building C object src/Libraries/CMakeFiles/3D_LIB.dir/3D/Source/alloc.c.o
[ 83%] Building C object src/Libraries/CMakeFiles/3D_LIB.dir/3D/Source/Bitmap.c.o
[ 83%] Building C object src/Libraries/CMakeFiles/3D_LIB.dir/3D/Source/clip.c.o
[ 83%] Building C object src/Libraries/CMakeFiles/3D_LIB.dir/3D/Source/detail.c.o
[ 83%] Building C object src/Libraries/CMakeFiles/3D_LIB.dir/3D/Source/fov.c.o
[ 84%] Building C object src/Libraries/CMakeFiles/3D_LIB.dir/3D/Source/GlobalV.c.o
[ 84%] Building C object src/Libraries/CMakeFiles/3D_LIB.dir/3D/Source/instance.c.o
[ 84%] Building C object src/Libraries/CMakeFiles/3D_LIB.dir/3D/Source/interp.c.o
/home/user/SRC/systemshock/src/Libraries/3D/Source/interp.c: In function ‘do_getparms’:
/home/user/SRC/systemshock/src/Libraries/3D/Source/interp.c:869:29: error: invalid operands to binary + (have ‘va_list’ {aka ‘__va_list’} and ‘int’)
869 | src = (long *)(parm_ptr + (*(unsigned short *)(opcode + 4)));
| ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
| |
| short unsigned int
/home/user/SRC/systemshock/src/Libraries/3D/Source/interp.c: In function ‘do_getparms_i’:
/home/user/SRC/systemshock/src/Libraries/3D/Source/interp.c:887:29: error: invalid operands to binary + (have ‘va_list’ {aka ‘__va_list’} and ‘int’)
887 | src = (long *)(parm_ptr + (*(unsigned short *)(opcode + 4)));
| ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
| |
| short unsigned int
make[2]: *** [src/Libraries/CMakeFiles/3D_LIB.dir/build.make:154: src/Libraries/CMakeFiles/3D_LIB.dir/3D/Source/interp.c.o] Error 1
make[1]: *** [CMakeFiles/Makefile2:308: src/Libraries/CMakeFiles/3D_LIB.dir/all] Error 2
make: *** [Makefile:84: all] Error 2

The same code builds just fine on Ubuntu 18.04 x86_64