I'm facing the same issue and did some tracing.
When I take a look into this file, script file when we perform "./lampp oci8";
/opt/lampp_181/share/lampp/oci8install
I found out that it wasn't looking for "libclntsh.so" actually but "libclntsh.so.10*"
libclntsh=`find $ora_home -name "libclntsh.so.10*" | head -1`
Try to create a softlink "libclntsh.so.10.1 -> libclntsh.so" and "libclntsh.so -> libclntsh.so.11.1" as below;
lrwxrwxrwx 1 oracle dba 69 2013-12-24 10:46 libclntsh.so -> /home/oracle/app/oracle/product/11.2.0/client_2/lib/libclntsh.so.11.1*
lrwxrwxrwx 1 oracle dba 64 2013-12-24 10:46 libclntsh.so.10.1 -> /home/oracle/app/oracle/product/11.2.0/client_2/lib/libclntsh.so*
-rwxr-xr-x 1 oracle dba 39997991 2013-12-24 10:46 libclntsh.so.11.1*
Never try that before but I saw this in the full Oracle Client lib dir.
One thing for sure, my XAMPP is running fine when I point oci8 to this location.
Oracle Run-time Client Library Version 11.2.0.1.0
my phpinfo() output