ARROW-2721: [C++] Fix ORC and Protocol Buffers link error

It's introduced at 408aa5a by me.
Sorry.

Author: Kouhei Sutou <kou@clear-code.com>

Closes #2146 from kou/cpp-fix-orc-and-protobuf-link-error and squashes the following commits:

725d783 <Kouhei Sutou>  Fix ORC and Protocol Buffers link error

Author: kou

cpp/CMakeLists.txt

@@ -593,9 +593,6 @@ if (ARROW_WITH_GRPC)
 endif()
 
 if (ARROW_ORC)
-  SET(ARROW_STATIC_LINK_LIBS
-    orc
-    ${ARROW_STATIC_LINK_LIBS})
   if (ARROW_PROTOBUF_USE_SHARED)
     SET(ARROW_LINK_LIBS
       protobuf
@@ -605,6 +602,9 @@ if (ARROW_ORC)
       protobuf
       ${ARROW_STATIC_LINK_LIBS})
   endif()
+  SET(ARROW_STATIC_LINK_LIBS
+    orc
+    ${ARROW_STATIC_LINK_LIBS})
 endif()
 
 if (ARROW_STATIC_LINK_LIBS)