You can gain more control on the codegen process by using a configuration object. Here's how you can create a debug build:
cfg = svdpiConfiguration;
cfg.CoderConfiguration.BuildConfiguration = 'Debug';
dpigen -config cfg -d MyDPIProject -testbench fun_tb.m fun.m -args {double(0),int8(0)} -launchreport
Here's the resulting compilation commands from the codegen report (with the mingw toolchain):
### Using toolchain: MinGW64 | gmake (64-bit Windows)
### Creating 'C:\dpigen_debug_mode\MyDPIProject\fun_rtw.mk' ...
### Building 'libfun_dpi': "$(MINGW_ROOT)\mingw32-make.exe" -j 6 -l 6 -Oline -f fun_rtw.mk all
"C:\Mingw64\bin/gcc" -c -fwrapv -m64 -O0 -g -msse2 -fno-predictive-commoning -D__USE_MINGW_ANSI_STDIO=1 -DMODEL=libfun_dpi @fun_rtw_comp.rsp -o "fun.obj" "C:/dpigen_debug_mode/MyDPIProject/fun.c"
"C:\Mingw64\bin/gcc" -c -fwrapv -m64 -O0 -g -msse2 -fno-predictive-commoning -D__USE_MINGW_ANSI_STDIO=1 -DMODEL=libfun_dpi @fun_rtw_comp.rsp -o "fun_dpi.obj" "C:/dpigen_debug_mode/MyDPIProject/fun_dpi.c"
"### Creating dynamic library "./libfun_dpi.dll" ..."
"C:\Mingw64\bin/g++" -shared -Wl,--no-undefined -g -Wl,--out-implib,./libfun_dpi.lib fun.def -o ./libfun_dpi.dll @fun_rtw.rsp -lws2_32
"### Created: ./libfun_dpi.dll"
"### Successfully generated all binary outputs."
You could also hand-edit the "fun_rtw.mk" makefile and reinvoke the "all" target if you are comfortable doing that.