XMLStarlet command line XML toolkit

There are multiple link errors like this:

/usr/lib/libexslt.a(crypto.o): In function `exsltCryptoGcryptInit':
(.text+0x15c): undefined reference to `gcry_check_version'

This is because the hand-crafted static linking performed in configure.in
does not include the necessary crypto libraries. In any case, when not
using a specific local version of libxslt etc., the dynamic libraries
returned by pkg-config should be used. Dynamic libraries bring in their own
dependencies as needed.

This patch does not attempt to fix the static linking situation.