add function types to arm crt assembly

[musl] / arch / arm / crt_arch.h

__asm__("\
.global _start \n\
.type _start,%function \n\
_start: \n\
        mov fp, #0 \n\
        mov lr, #0 \n\
        mov a1, sp \n\
        and sp, sp, #-16 \n\
        bl __cstart \n\
");