define checkdef
`if echo 'int main(){(void)$(1);}' | \
    gcc -include stdio.h -xc - -o/dev/null 2>/dev/null; \
 then \
     echo 1; \
 else \
     echo 0; \
 fi`
endef

my-mv:: CFLAGS=-std=gnu99 -D_GNU_SOURCE -DHAVE_RENAMEAT2=$(call checkdef,renameat2) -DHAVE_COPY_FILE_RANGE=$(call checkdef,copy_file_range)