Function to_upper

Sming/System/m_printf.cpp:31–34

#define is_print(c) ((c) >= ' ' && (c) <= '~')

static char to_upper(char c)
{
    return (c >= 'a' && c <= 'z') ? (c + 'A' - 'a') : c;
}

static void str_upper(char* s)
{