The one you want is -t gui...
This is a fairly complete list of switches for bmk and bcc for those who might need it:
bmk
makemod [module]
makeapp [switches] filename
-t type : set executable type
console
gui
-a : rebuild all
-x : run
-k : kill ?
-g arch : set architechture
x86
ppc
-f module : set framework
-o file : set outputfile
-s host : set server address
-u name : set user name
-p pwd : set password
-y proxy : set proxy
-b stub : set appstub
-d : debug mode
-r : release mode
-q : quiet mode
-v : verbose mode
-z : trace headers
bcc
-t type : set executable type
console
gui
-f module : set framework
-g arch : set architechture
x86
ppc
-m name : set module name
-q : quiet mode
-v : verbose mode
-r : release mode
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