Linux cmake script env doesn't have pushd/popd.

Author: cwillmor

cmake/modules/AddSwift.cmake

@@ -623,10 +623,10 @@ function(_target_merge_static_library dst_target src_target)
   set(unpack_dir "${CMAKE_BINARY_DIR}/tmp/unpack/${dst_target}")
   add_custom_command(TARGET "${dst_target}" POST_BUILD
     COMMAND "${CMAKE_COMMAND}" -E make_directory "${unpack_dir}"
-    COMMAND pushd "${unpack_dir}"
+    COMMAND cd "${unpack_dir}"
     COMMAND "${CMAKE_AR}" -x "$<TARGET_FILE:${src_target}>"
     COMMAND "${CMAKE_AR}" -r "$<TARGET_FILE:${dst_target}>" ./*.o
-    COMMAND popd
+    COMMAND cd "${CMAKE_BINARY_DIR}"
     COMMAND "${CMAKE_COMMAND}" -E remove_directory "${unpack_dir}"
   )
 endfunction()