io-watchdog-interposer can't find libc.so

[grondo]

libc.so.* is no longer typically kept under /lib or /lib64 as assumed in the io-watchdog code.
Need a better scheme for finding the "real" libc write call symbols.

Since we've interposed the write calls in our LD_PRELOAD library, when libc can't be found the code cannot currently print an error, it instead silently exits with code 15.