Swift: support `-rpath` for executables

This adjusts the flags to enable setting the RPATH for executables.

Modules/CMakeSwiftInformation.cmake

@@ -29,6 +29,11 @@ endif()
 if(NOT CMAKE_SYSTEM_NAME STREQUAL Windows)
   set(CMAKE_SHARED_LIBRARY_RUNTIME_Swift_FLAG "-Xlinker -rpath -Xlinker ")
   set(CMAKE_SHARED_LIBRARY_RUNTIME_Swift_FLAG_SEP ":")
+
+  if(NOT CMAKE_SYSTEM_NAME STREQUAL Darwin)
+    set(CMAKE_EXECUTABLE_RUNTIME_Swift_FLAG "-Xlinker -rpath -Xlinker ")
+    set(CMAKE_EXECUTABLE_RUNTIME_Swift_FLAG_SEP ":")
+  endif()
 endif()
 
 set(CMAKE_Swift_COMPILE_OPTIONS_TARGET "-target ")