Add CMakeLists.txt for sftp

src/sftp/CMakeLists.txt

+# not currently used
+
+project (SFTP C)
+
+cmake_minimum_required(VERSION 3.11)
+
+set(SOURCE
+	sftp_attr.c
+	sftp_client.c
+	sftp_pkt.c
+	sftp_server.c
+	sftp_str.c
+)
+
+set(HEADER
+	sftp_internal.h
+	sftp_static.h
+	sftp.h
+)
+
+add_library(sftp OBJECT ${SOURCE})
+target_compile_features(sftp PUBLIC c_std_99)
+target_include_directories(sftp PUBLIC ${CMAKE_CURRENT_SOURCE_DIR})
+target_link_libraries(sftp xpdev)