Fix a bug in printf()

stdlib: implement strtoul() and strtol() using a macro

Because we were previously converting the bytes in the format
string into Rust's char type and then printing that using the
format machinery, byte values that were not valid single-byte
UTF-8 characters failed to print correctly.  I found this while
trying to implement qsort() because the output of my test program
was mysteriously incorrect despite it working when I used glibc.

Signed-off-by: Marat Safin <jeizsm@gmail.com>

add gmtime and difftime

ci: Ensure that the correct compiler is installed

Ensure that a compiler is installed when the aarch64 CI build is run.

Run ./fmt.sh

Add mem* functions to stdio
Add constant int functions

stdio: Implement rename