On my macppc machine I did the following:
1: Upgraded the kernel from 1.5H to 1.5Q. Worked fine with 1.5H userland.
2: Built the world. Worked fine.
3: Installed. Worked fine.
4: Proceeded to a `make release', which fell over with 'Internal 
compiler error: Program cc1 got fatal signal 11' in the kernel build 
phase. Re-running make in the kernel build directory got me a few 
files further, but then the error occurred again. Subsequently the 
machine crashed (hard) without leaving any messages.
I haven't really stressed the machine much since the upgrade. CVS 
updates proceed without error, but builds fail randomly. The machine 
has crashed (again without any messages on the X console) a few times 
during `make build'. I disabled soft dependencies, but that didn't 
help a thing.
This is how things tend to look:

-DLKM -DDIAGNOSTIC -DTRAP_PANICWAIT -DNMBCLUSTERS="0x400" -DMAXUSERS=32
-D_KERNEL -Dmacppc  -c ../../../../netinet/tcp_input.c
cpp: cc: Internal compiler error: program cc1 got fatal signal 5
*** Error code 1

Stop.
fkmac26(25)$ make
[...]
output pipe has been closed
-DLKM -DDIAGNOSTIC -DTRAP_PANICWAIT -DNMBCLUSTERS="0x400" -DMAXUSERS=32
-D_KERNEL -Dmacppc  -c ../../../../nfs/nfs_serv.c
cpp: cc: Internal compiler error: program cc1 got fatal signal 5
*** Error code 1

Stop.
output pipe has been closed
fkmac26(29)$ {standard input}: Assembler messages:
{standard input}:12919: Warning: end of file not at end of a line; newline
inserted
fkmac26(29)$ rm nfs_serv.o
fkmac26(30)$ make
cc  -O2 -pipe -Werror -Wreturn-type -Wpointer-arith -Wno-uninitialized
-Wno-main -msoft-float -I. -I../../../../arch -I../../../.. -nostdinc
-DLKM -DDIAGNOSTIC -DTRAP_PANICWAIT -DNMBCLUSTERS="0x400" -DMAXUSERS=32
-D_KERNEL -Dmacppc  -c ../../../../nfs/nfs_serv.c
cpp: cc: Internal compiler error: program cc1 got fatal signal 11
*** Error code 1

Hans-Christian
-- 
Dr. Hans-Christian Becker (hcb@phc.chalmers.se)
Department of Physical Chemistry
Chalmers University of Technology, Sweden