You can use the `-S` switch with gcc to produce the intermediate assembler representation of your C program instead of binary output. From there you can see for yourself what optimisation has been performed and what hand optimisations are possible.

I just compiled my own 'hello.c' on Linux, with the optimisation flag set for 'code size', and the binary weighed in around 8.3k. I then removed the `printf` call and the inclusion of `stdio.h`. The resulting binary was 8.1k. This is exactly as expected. Why would the inclusion of a call to a dynamic library bloat the final binary size?