Bug 22643

If the following is included in the kernel config file:
device gus0 at isa? port 0x220 irq 12 drq 1

I get these errors:
isa_compat.o: In function `isa_compat_nextid':
/usr/src/sys/compile/NEUMANN/../../i386/isa/isa_compat.c:61: undefined reference to `gusdriver'
midi_synth.o: In function `midi_outc':
/usr/src/sys/compile/NEUMANN/../../i386/isa/sound/midi_synth.c(.text+0x4d): undefined reference to `midi_devs'
midi_synth.o: In function `prefix_cmd':
/usr/src/sys/compile/NEUMANN/../../i386/isa/sound/midi_synth.c:133: undefined reference to `midi_devs'
midi_synth.o: In function `midi_synth_input':
/usr/src/sys/compile/NEUMANN/../../i386/isa/sound/midi_synth.c(.text+0xdd): undefined reference to `num_midis'
/usr/src/sys/compile/NEUMANN/../../i386/isa/sound/midi_synth.c(.text+0xff): undefined reference to `midi_devs'
midi_synth.o: In function `leave_sysex':
/usr/src/sys/compile/NEUMANN/../../i386/isa/sound/midi_synth.c(.text+0x2c6): undefined reference to `synth_devs'
/usr/src/sys/compile/NEUMANN/../../i386/isa/sound/midi_synth.c(.text+0x2ef): undefined reference to `midi_devs'
midi_synth.o: In function `midi_synth_ioctl':
/usr/src/sys/compile/NEUMANN/../../i386/isa/sound/midi_synth.c:272: undefined reference to `synth_devs'
midi_synth.o: In function `midi_synth_kill_note':
/usr/src/sys/compile/NEUMANN/../../i386/isa/sound/midi_synth.c(.text+0x383): undefined reference to `synth_devs'
midi_synth.o: In function `midi_synth_set_instr':
/usr/src/sys/compile/NEUMANN/../../i386/isa/sound/midi_synth.c:333: undefined reference to `synth_devs'
midi_synth.o: In function `midi_synth_start_note':
/usr/src/sys/compile/NEUMANN/../../i386/isa/sound/midi_synth.c(.text+0x512): undefined reference to `synth_devs'
midi_synth.o: In function `midi_synth_open':
/usr/src/sys/compile/NEUMANN/../../i386/isa/sound/midi_synth.c(.text+0x5f3): undefined reference to `synth_devs'
/usr/src/sys/compile/NEUMANN/../../i386/isa/sound/midi_synth.c(.text+0x600): undefined reference to `num_midis'
/usr/src/sys/compile/NEUMANN/../../i386/isa/sound/midi_synth.c(.text+0x630): undefined reference to `midi_devs'
midi_synth.o: In function `midi_synth_close':
/usr/src/sys/compile/NEUMANN/../../i386/isa/sound/midi_synth.c:426: undefined reference to `synth_devs'
/usr/src/sys/compile/NEUMANN/../../i386/isa/sound/midi_synth.c:433: undefined reference to `midi_devs'
midi_synth.o: In function `midi_synth_load_patch':
/usr/src/sys/compile/NEUMANN/../../i386/isa/sound/midi_synth.c:447: undefined reference to `synth_devs'
/usr/src/sys/compile/NEUMANN/../../i386/isa/sound/midi_synth.c:509: undefined reference to `midi_devs'
midi_synth.o: In function `midi_synth_aftertouch':
/usr/src/sys/compile/NEUMANN/../../i386/isa/sound/midi_synth.c(.text+0x912): undefined reference to `synth_devs'
midi_synth.o: In function `midi_synth_controller':
/usr/src/sys/compile/NEUMANN/../../i386/isa/sound/midi_synth.c(.text+0x9aa): undefined reference to `synth_devs'
midi_synth.o: In function `midi_synth_bender':
/usr/src/sys/compile/NEUMANN/../../i386/isa/sound/midi_synth.c(.text+0xa66): undefined reference to `synth_devs'
midi_synth.o: In function `midi_synth_send_sysex':
/usr/src/sys/compile/NEUMANN/../../i386/isa/sound/midi_synth.c(.text+0xb23): undefined reference to `synth_devs'
/usr/src/sys/compile/NEUMANN/../../i386/isa/sound/midi_synth.c(.text+0xbc9): undefined reference to `midi_devs'
/usr/src/sys/compile/NEUMANN/../../i386/isa/sound/midi_synth.c(.text+0xc12): undefined reference to `midi_devs'
*** Error code 1

Fix: 

I have been looking at the source and I'm not able to locate the reference problem betweene the header files and the c-source.
I believe it has to do with of the general sound or isa code.
How-To-Repeat: Include the mentioned gus0 in kernel.