Building cross/avr-gcc with CC=clang

[Edgar Fuß <ef%math.uni-bonn.de@localhost>]

I'm trying to build cross/avr-gcc with clang (on OSX) and get:

.../cross/avr-gcc/work/gcc-4.4.1/gcc/toplev.c:536:1: error: redefinition of a 
'extern inline'
      function 'floor_log2' is not supported in C99 mode
floor_log2 (unsigned HOST_WIDE_INT x)
^
In file included from .../cross/avr-gcc/work/gcc-4.4.1/gcc/toplev.c:58:
.../cross/avr-gcc/work/gcc-4.4.1/gcc/toplev.h:190:1: note: previous definition 
is here
floor_log2 (unsigned HOST_WIDE_INT x)
^
.../cross/avr-gcc/work/gcc-4.4.1/gcc/toplev.c:571:1: error: redefinition of a 
'extern inline'
      function 'exact_log2' is not supported in C99 mode
exact_log2 (unsigned HOST_WIDE_INT x)
^
In file included from .../cross/avr-gcc/work/gcc-4.4.1/gcc/toplev.c:58:
.../cross/avr-gcc/work/gcc-4.4.1/gcc/toplev.h:196:1: note: previous definition 
is here
exact_log2 (unsigned HOST_WIDE_INT x)
^

Any clues?