[Build System: CMake] Set the install_name_dir to @rpath for the SwiftLang module in SourceKit.

(cherry picked from commit d332d21)

Author: Rostepher

tools/SourceKit/tools/swift-lang/CMakeLists.txt

@@ -28,6 +28,7 @@ if(NOT SWIFT_SOURCEKIT_USE_INPROC_LIBRARY AND SWIFT_BUILD_STDLIB AND SWIFT_BUILD
     PRIVATE_LINK_LIBRARIES ${SOURCEKITD_LINK_LIBS}
     SWIFT_COMPILE_FLAGS ${EXTRA_COMPILE_FLAGS}
     INSTALL_IN_COMPONENT ${INSTALLED_COMP}
+    DARWIN_INSTALL_NAME_DIR "@rpath"
     TARGET_SDKS ${SOURCEKIT_DEFAULT_TARGET_SDK}
     IS_STDLIB)
 endif()