fix linker error with -O0 and c99

This patch fixes linker failure with -O0 -std=c99 options:
cc -O0 -g -Wall -std=c99 demo.c -o demo
/tmp/cc9G1r7e.o: In function `sorter_tim_sort':
/local/git/sort/sort.h:683: undefined reference to `compute_minrun'
collect2: error: ld returned 1 exit status
make: *** [demo] Error 1

Similar issue is discussed here: http://stackoverflow.com/questions/6312597/is-inline-without-static-or-extern-ever-useful-in-c99