I tested it on linux and I have this problem (since r16, r15 is ok) :
/root/devkitARMr17/bin/../lib/gcc/arm-elf/4.0.2/../../../../arm-elf/lib/libc.a(sbrkr.o): In function `_sbrk_r':
: undefined reference to `_sbrk'
/root/devkitARMr17/bin/../lib/gcc/arm-elf/4.0.2/../../../../arm-elf/lib/libc.a(makebuf.o): In function `__smakebuf':
: undefined reference to `isatty'
/root/devkitARMr17/bin/../lib/gcc/arm-elf/4.0.2/../../../../arm-elf/lib/libc.a(writer.o): In function `_write_r':
: undefined reference to `_write'
/root/devkitARMr17/bin/../lib/gcc/arm-elf/4.0.2/../../../../arm-elf/lib/libc.a(closer.o): In function `_close_r':
: undefined reference to `_close'
/root/devkitARMr17/bin/../lib/gcc/arm-elf/4.0.2/../../../../arm-elf/lib/libc.a(fstatr.o): In function `_fstat_r':
: undefined reference to `_fstat'
/root/devkitARMr17/bin/../lib/gcc/arm-elf/4.0.2/../../../../arm-elf/lib/libc.a(lseekr.o): In function `_lseek_r':
: undefined reference to `_lseek'
/root/devkitARMr17/bin/../lib/gcc/arm-elf/4.0.2/../../../../arm-elf/lib/libc.a(readr.o): In function `_read_r':
: undefined reference to `_read'
collect2: ld returned 1 exit status