clang warning with ptrace pid_read() utils

[mothran]

../../contrib/ecfs/src/core_text.c:37:12: warning: implicit declaration of function 'pid_read' is invalid in C99 [-Wimplicit-function-declaration]
        int ret = pid_read(pid, (void *)ptr, (void *)vaddr, len);
                  ^
../../contrib/ecfs/src/core_text.c:32:16: warning: unused function 'ptrace_read_mem' [-Wunused-function]
static ssize_t ptrace_read_mem(pid_t pid, uint8_t *ptr, unsigned long vaddr, size_t len)
               ^

[elfmaster]

ptrace_read_mem() may be used for the snapshot functionality I'm working on. I'll add a prototype for the other one.