build: stage a copy in the old installation location

The shared library was previously built and installed into the swift
resource directory.  Replicate this behaviour for the integration tests.

Author: compnerd

CMakeLists.txt

@@ -142,4 +142,9 @@ install(FILES
           ${CMAKE_CURRENT_BINARY_DIR}/${CMAKE_SHARED_LIBRARY_PREFIX}XCTest${CMAKE_SHARED_LIBRARY_SUFFIX}
         DESTINATION
           ${CMAKE_INSTALL_FULL_LIBDIR})
+# NOTE(compnerd) stage a compatibility copy in the swift resource dir
+install(FILES
+          ${CMAKE_CURRENT_BINARY_DIR}/${CMAKE_SHARED_LIBRARY_PREFIX}XCTest${CMAKE_SHARED_LIBRARY_SUFFIX}
+        DESTINATION
+          ${CMAKE_INSTALL_FULL_LIBDIR}/swift/${SWIFT_OS})