@User Okay, partial victory. Since all the errors were warnings about implicit function declaration, I used this string in the CFLAGS in defs.mak: -Wno-error=implicit-function-declaration
That converted the errors back into warnings, and the object files were created. However, make did stop prematurely:
--- linking libtcltk.o
--- compiling magic/magicTop.o
magicTop.c:53:5: warning: implicit declaration of function 'magicMain' [-Wimplicit-function-declaration]
--- linking libmagic.o
--- making Tcl shared libraries
make: * No rule to make target `../extract/libextract.o', needed by `tclmagic.dylib'. Stop.