Remove special handling of script search path on Windows

Remove special handling of script search path on Windows

On all platforms, search for scripts in
$HOME/.openocd
${run_prefix}${pkgdatadir}/site
${run_prefix}${pkgdatadir}/scripts

On Windows, set run_prefix to the runtime path of the executable, minus
${bindir}. This is to enable the install dir to be moved anywhere, as long
as the structure of the install dir is kept intact. On all other platforms,
run_prefix is empty.

The script paths can now be adjusted on Windows builds the normal way; by
overriding pkgdatadir at build time. For example, to create a Windows
package layout of

bin/openocd.exe
scripts/interface/...
scripts/target/...

you can do
configure --prefix= --enable-... and then
make pkgdatadir= DESTDIR=/some/path clean all install

Also, remove the unused PKGLIBDIR define.

Change-Id: If2c8228fc80c598d763efad21c5f51695ff9b6cf
Signed-off-by: Andreas Fritiofson <andreas.fritiofson@gmail.com>
Reviewed-on: http://openocd.zylin.com/1796
Tested-by: jenkins
Reviewed-by: Jens Bauer <jens@gpio.dk>
Reviewed-by: Spencer Oliver <spen@spen-soft.co.uk>