ARROW-6742: [C++] Remove boost::filesystem dependency in hdfs_internal.cc

Closes #6062 from pitrou/ARROW-6742-hdfs-boost-fs and squashes the following commits:

250178e <Antoine Pitrou> ARROW-6742:  Remove boost::filesystem dependency in hdfs_internal.cc

Authored-by: Antoine Pitrou <antoine@python.org>
Signed-off-by: Sutou Kouhei <kou@clear-code.com>

Author: pitrou

.github/workflows/cpp.yml

@@ -99,6 +99,7 @@ jobs:
       # TODO(kszucs): link error in the tests
       ARROW_ORC: OFF
       ARROW_FLIGHT: ON
+      ARROW_HDFS: ON
       ARROW_PLASMA: ON
       ARROW_GANDIVA: ON
       ARROW_PARQUET: ON
@@ -143,6 +144,7 @@ jobs:
       CMAKE_INSTALL_PREFIX: /usr
       ARROW_HOME: /usr
       ARROW_FLIGHT: OFF
+      ARROW_HDFS: ON
       ARROW_PARQUET: OFF
       ARROW_WITH_ZLIB: OFF
       ARROW_WITH_LZ4: OFF

cpp/CMakeLists.txt

@@ -679,10 +679,8 @@ endif()
 
 set(ARROW_SHARED_PRIVATE_LINK_LIBS ${ARROW_STATIC_LINK_LIBS})
 
-# boost::filesystem is needed for HDFS, and for S3 and Flight tests as a
-# boost::process dependency.
-if(((ARROW_FLIGHT OR ARROW_S3) AND (ARROW_BUILD_TESTS OR ARROW_BUILD_INTEGRATION))
-   OR ARROW_HDFS)
+# boost::filesystem is needed for S3 and Flight tests as a boost::process dependency.
+if(((ARROW_FLIGHT OR ARROW_S3) AND (ARROW_BUILD_TESTS OR ARROW_BUILD_INTEGRATION)))
   set(ARROW_WITH_BOOST_FILESYSTEM ON)
 
   list(APPEND ARROW_SHARED_PRIVATE_LINK_LIBS ${BOOST_FILESYSTEM_LIBRARY}