De-POSIXify the shell usage in gen-avr-lib-tree.sh, since Solaris' /bin/sh is not POSIX-aware. For the remaining tools, their POSIXish variants can be chosen by prepending the PATH with /usr/xpg4/bin (doesn't harm for non-Solaris systems), but as for the shell this script is running under, the only other option were to let autoconf detect it, which is a bit of overkill.
Changed paths: