Ok, tried again today with a -t fbpc -no-asm.
I get this :
bash-2.02$ make
gcc "src/MINEM68K.c" -o "bld/MINEM68K.o" -c -Wall -Wmissing-prototypes -Wno-uninitialized -Wundef -Wstrict-prototypes -Os
gcc: installation problem, cannot exec `cpp-precomp': No such file or directory
make: *** [bld/MINEM68K.o] Error 1
bash-2.02$
So I suppose there is something wrong with my GCC installation :/
Then tried a -t xgen -no-asm on another rhapsody machine with no other compilers than the Apple OSX server dev tools.
Note the X11 server is installed in /Local/Library/Xnext/X11R6.4, with a symlink in /usr/X11R6.4 . So I changed the line ,
$(ObjFiles) -L/usr/X11R6/lib -lX11
into
$(ObjFiles) -L/usr/X11R6.4/lib -lX11
this is what I get :
bash-2.02$ make
cc "src/MINEM68K.c" -o "bld/MINEM68K.o" -c
cc "src/MYOSGLUE.c" -o "bld/MYOSGLUE.o" -c
src/CNFGRAPI.h:16: header file 'X11/Xlib.h' not found
src/CNFGRAPI.h:17: header file 'X11/Xutil.h' not found
src/CNFGRAPI.h:18: header file 'X11/keysym.h' not found
src/CNFGRAPI.h:19: header file 'X11/keysymdef.h' not found
src/CNFGRAPI.h:20: header file 'X11/Xatom.h' not found
src/MYOSGLUE.c:189: undefined type, found `Display'
src/MYOSGLUE.c:210: undefined type, found `Atom'
src/MYOSGLUE.c:210: illegal external declaration, missing `;' after `)'
src/MYOSGLUE.c:212: undefined type, found `Atom'
src/MYOSGLUE.c:212: illegal external declaration, missing `;' after `)'
src/MYOSGLUE.c:213: undefined type, found `Atom'
src/MYOSGLUE.c:213: illegal external declaration, missing `;' after `)'
src/MYOSGLUE.c:214: undefined type, found `Atom'
src/MYOSGLUE.c:214: illegal external declaration, missing `;' after `)'
src/MYOSGLUE.c:215: undefined type, found `Atom'
src/MYOSGLUE.c:215: illegal external declaration, missing `;' after `)'
src/MYOSGLUE.c:216: undefined type, found `Atom'
src/MYOSGLUE.c:216: illegal external declaration, missing `;' after `)'
src/MYOSGLUE.c:217: undefined type, found `Atom'
src/MYOSGLUE.c:217: illegal external declaration, missing `;' after `)'
src/MYOSGLUE.c:218: undefined type, found `Atom'
src/MYOSGLUE.c:218: illegal external declaration, missing `;' after `)'
src/MYOSGLUE.c:219: undefined type, found `Atom'
src/MYOSGLUE.c:219: illegal external declaration, missing `;' after `)'
src/MYOSGLUE.c:220: undefined type, found `Atom'
src/MYOSGLUE.c:220: illegal external declaration, missing `;' after `)'
src/MYOSGLUE.c:221: undefined type, found `Atom'
src/MYOSGLUE.c:221: illegal external declaration, missing `;' after `)'
src/MYOSGLUE.c:222: undefined type, found `Atom'
src/MYOSGLUE.c:222: illegal external declaration, missing `;' after `)'
src/MYOSGLUE.c:223: undefined type, found `Atom'
src/MYOSGLUE.c:223: illegal external declaration, missing `;' after `)'
src/MYOSGLUE.c:224: undefined type, found `Atom'
src/MYOSGLUE.c:224: illegal external declaration, missing `;' after `)'
src/MYOSGLUE.c:225: undefined type, found `Atom'
src/MYOSGLUE.c:225: illegal external declaration, missing `;' after `)'
src/MYOSGLUE.c:228: undefined type, found `Atom'
src/MYOSGLUE.c:228: illegal external declaration, missing `;' after `)'
src/MYOSGLUE.c:229: undefined type, found `Atom'
src/MYOSGLUE.c:229: illegal external declaration, missing `;' after `)'
src/MYOSGLUE.c:230: undefined type, found `Atom'
src/MYOSGLUE.c:230: illegal external declaration, missing `;' after `)'
src/MYOSGLUE.c:266: undefined type, found `Atom'
src/MYOSGLUE.c:272: undefined type, found `Atom'
src/MYOSGLUE.c:279: undefined type, found `Window'
src/MYOSGLUE.c:293: undefined type, found `Atom'
src/MYOSGLUE.c:293: illegal expression, found `)'
src/MYOSGLUE.c:293: syntax error, missing `;' after `)'
src/MYOSGLUE.c

undefined type, found `Window'
src/MYOSGLUE.c

undefined type, found `GC'
src/MYOSGLUE.c

undefined type, found `XColor'
src/MYOSGLUE.c

undefined type, found `XColor'
src/MYOSGLUE.c

undefined type, found `XImage'
src/MYOSGLUE.c

undefined type, found `XImage'
src/MYOSGLUE.c

undefined type, found `XImage'
src/MYOSGLUE.c

undefined type, found `Cursor'
src/MYOSGLUE.c

undefined type, found `Window'
src/MYOSGLUE.c

undefined type, found `Pixmap'
src/MYOSGLUE.c

undefined type, found `XGCValues'
src/MYOSGLUE.c

undefined type, found `GC'
src/MYOSGLUE.c

undefined type, found `Window'
src/MYOSGLUE.c

undefined type, found `Window'
src/MYOSGLUE.c

undefined type, found `Window'
src/MYOSGLUE.c

undefined type, found `Window'
src/MYOSGLUE.c

undefined type, found `KeyCode'
src/MYOSGLUE.c

undefined type, found `KeySym'
src/MYOSGLUE.c

undefined type, found `KeyCode'
src/MYOSGLUE.c

undefined type, found `Window'
src/MYOSGLUE.c

undefined type, found `Window'
src/MYOSGLUE.c

undefined type, found `XKeyboardState'
src/MYOSGLUE.c

undefined type, found `XKeyboardControl'
src/MYOSGLUE.c

undefined type, found `XKeyboardControl'
src/MYOSGLUE.c

undefined type, found `XEvent'
src/MYOSGLUE.c

undefined type, found `Window'
src/MYOSGLUE.c

undefined type, found `XEvent'
src/MYOSGLUE.c

undefined type, found `Atom'
src/MYOSGLUE.c

undefined type, found `XEvent'
src/MYOSGLUE.c

undefined type, found `Atom'
src/MYOSGLUE.c

undefined type, found `Time'
src/MYOSGLUE.c

undefined type, found `XEvent'
src/MYOSGLUE.c

undefined type, found `Window'
src/MYOSGLUE.c

undefined type, found `Window'
src/MYOSGLUE.c

undefined type, found `XEvent'
src/MYOSGLUE.c

undefined type, found `Atom'
src/MYOSGLUE.c

undefined type, found `XEvent'
src/MYOSGLUE.c

undefined type, found `XEvent'
src/MYOSGLUE.c

undefined type, found `XEvent'
src/MYOSGLUE.c

undefined type, found `Window'
src/MYOSGLUE.c

undefined type, found `Window'
src/MYOSGLUE.c

undefined type, found `XEvent'
src/MYOSGLUE.c

undefined type, found `Time'
src/MYOSGLUE.c

illegal statement, missing `;' after `)'
src/MYOSGLUE.c

undefined type, found `XEvent'
src/MYOSGLUE.c

undefined type, found `XEvent'
src/MYOSGLUE.c

undefined type, found `Window'
src/MYOSGLUE.c

undefined type, found `Colormap'
src/MYOSGLUE.c

undefined type, found `Visual'
src/MYOSGLUE.c

undefined type, found `Window'
src/MYOSGLUE.c

undefined type, found `Window'
src/MYOSGLUE.c

undefined type, found `XSetWindowAttributes'
src/MYOSGLUE.c

undefined type, found `XClassHint'
src/MYOSGLUE.c

undefined type, found `XWMHints'
src/MYOSGLUE.c

undefined type, found `XSizeHints'
src/MYOSGLUE.c

undefined type, found `Window'
src/MYOSGLUE.c

undefined type, found `GC'
src/MYOSGLUE.c

undefined type, found `Window'
src/MYOSGLUE.c

undefined type, found `Window'
src/MYOSGLUE.c

undefined type, found `Window'
src/MYOSGLUE.c:4064: undefined type, found `Window'
src/MYOSGLUE.c:4071: undefined type, found `Window'
src/MYOSGLUE.c:4148: undefined type, found `Window'
src/MYOSGLUE.c:4150: undefined type, found `Window'
src/MYOSGLUE.c:4423: undefined type, found `XEvent'
make: *** [bld/MYOSGLUE.o] Error 1