__uint128_t missing in gcc4, scalar_mode_supported_p not set?

[Olaf Hering]

glibc fails to build with gcc4 on powerpc-linux.

../sysdeps/unix/sysv/linux/powerpc/sys/procfs.h:57: error: syntax error before 'elf_vrreg_t'
../sysdeps/unix/sysv/linux/powerpc/sys/procfs.h:57: warning: type defaults to 'int' in declaration of 'elf_vrreg_t'
../sysdeps/unix/sysv/linux/powerpc/sys/procfs.h:57: warning: data definition has no type or storage class
../sysdeps/unix/sysv/linux/powerpc/sys/procfs.h:58: error: syntax error before 'elf_vrregset_t'
../sysdeps/unix/sysv/linux/powerpc/sys/procfs.h:58: warning: type defaults to 'int' in declaration of 'elf_vrregset_t'
../sysdeps/unix/sysv/linux/powerpc/sys/procfs.h:58: warning: data definition has no type or storage class
make[2]: *** [/usr/src/packages/BUILD/glibc-2.4/cc/nptl-struct-pthread.h] Error 1

It seems gcc-head/gcc/c-common.c is the place to add the missing
__uint128_t.  But gcc4 has a new targetm.scalar_mode_supported_p, I dont
see an assigment for that member anywhere?
Where is scalar_mode_supported_p supposed to be initalized?