Paul, Pete, thanks for the clarification.
Jantje, I had just downloaded the source of avr-gcc and found the same thing. I also found sin.S which (once you get past the license and checks for redefinition) is just
#include "fp32def.h"
#include "asmdef.h"
/* float sin (float A);
The sin() function returns the sine of A, where A is given in radians.
*/
ENTRY sin
push rA3
rcall _U(__fp_rempio2)
pop r0
sbrc r0, 7
subi ZL, -2
rjmp _U(__fp_sinus)
ENDFUNC