[CMake] Fix RUNPATH of lib_InternalSwiftScan in Linux
libSwiftScan is built in 'lib' but installed in 'lib/swift/host' RUNPATH
should have correct '$ORIGIN/../{platform}' to load 'swiftCore' runtime
library.
(cherry picked from commit 4ccc86661208d2874d89fdd83030f9f6ab0a4b39)
(cherry picked from commit 3badb3bfcd98490b9bf5f7cfb0958d9e7aeba0c9)
