Added libexpat 2.2.6

# Installation instructions

## Download Source

First download the source into directory `$DIR` (placeholder for the directory of your choice).

```bash

cd $DIR

wget https://github.com/libexpat/libexpat/archive/R_2_2_6.tar.gz

tar -xzf R_2_2_6.tar.gz

```

## Reconfigure with NEC-falvoured autotools

Trigger the autotools reconfiguration process. Unfortunately, the nec-flavoured autotools are installed only on the vector nodes. Hence, we need to run an interactive job on a vector node to do the job:

```bash

# start insteractive job

qlogin -q veinteractive -l elapstim_req=1800

# get autoreconf into PATH

export PATH="/opt/nec/ve/bin:$PATH"

cd $DIR/libexpat-R_2_2_6/expat

./buildconf.sh

exit

```

## Build and install

On the front-end, we can now cross-compile. Remember to replace `$PREFIX` with your installation directory.

```bash

# configure the package

./configure \

CC=ncc CFLAGS=-O3 CXX=nc++ FC=nfort F90=nfort AR=nar RANLIB=nranlib LD=nld \

--host=ve-nec-linux-gnu --prefix=$PREFIX

# buld and install library

make -C lib all install

```

To test the library, you have to start an interactive job

```bash

# start insteractive job

qlogin -q veinteractive -l elapstim_req=1800

cd $DIR/libexpat-R_2_2_6/expat

make -C tests check

exit

```