[xml] using clang: details

[Jim Meyering <jim meyering net>]

FYI, I built the tools described here:

  http://clang-analyzer.llvm.org/

Than ran them like this for libxml2:

    scan-build -o clang ./autogen.sh
    scan-build -o clang make

The resulting HTML:

  http://meyering.net/code/tmp/clang/libxml2-vs-clang-syntax-checker/index.html

is essentially the clang/ directory specified by the commands above.