Fixed to select correct library under 32 bit.

Library path was hard coded and this caused a problem that incorrect library file was selected under 32 bit environment.
This commit add some codes to choose corresponding library file according to the build environment.
Changed to use find_library

Changed the code to use find_library function instead of some hard coded paths.
Merge pull request #495 from mohammedari/fix-pxc-cmake

Fixing the problem that incorrect pxc library was selected under 32bit environment