Swift: support `INSTALL_NAME_DIR` on Darwin

Adjust the shared object rule to ensure that we honour the
`INSTALL_NAME_DIR` property on Swift targets.  This enables the use of
`INSTALL_NAME_DIR` and `BUILD_WITH_INSTALL_NAME_DIR` on Darwin with
Ninja.

Modules/CMakeSwiftInformation.cmake

@@ -76,7 +76,7 @@ if(CMAKE_SYSTEM_NAME STREQUAL Windows)
 endif()
 
 if(NOT CMAKE_Swift_CREATE_SHARED_LIBRARY)
-  set(CMAKE_Swift_CREATE_SHARED_LIBRARY "<CMAKE_Swift_COMPILER> -output-file-map <SWIFT_OUTPUT_FILE_MAP> -incremental -j ${CMAKE_Swift_NUM_THREADS} -emit-library -o <TARGET> -module-name <SWIFT_MODULE_NAME> -module-link-name <SWIFT_LIBRARY_NAME> -emit-module -emit-module-path <SWIFT_MODULE> -emit-dependencies <DEFINES> <FLAGS> <INCLUDES> <SWIFT_SOURCES> <LINK_FLAGS> <SONAME_FLAG> <TARGET_SONAME> ${CMAKE_Swift_IMPLIB_LINKER_FLAGS} <LINK_LIBRARIES>")
+  set(CMAKE_Swift_CREATE_SHARED_LIBRARY "<CMAKE_Swift_COMPILER> -output-file-map <SWIFT_OUTPUT_FILE_MAP> -incremental -j ${CMAKE_Swift_NUM_THREADS} -emit-library -o <TARGET> -module-name <SWIFT_MODULE_NAME> -module-link-name <SWIFT_LIBRARY_NAME> -emit-module -emit-module-path <SWIFT_MODULE> -emit-dependencies <DEFINES> <FLAGS> <INCLUDES> <SWIFT_SOURCES> <LINK_FLAGS> <SONAME_FLAG> <TARGET_INSTALLNAME_DIR><TARGET_SONAME> ${CMAKE_Swift_IMPLIB_LINKER_FLAGS} <LINK_LIBRARIES>")
 endif()
 
 if(NOT CMAKE_Swift_CREATE_SHARED_MODULE)