ENH: Conform GDCM to support CMAKE_*OUTPUT_DIRECTORY

Recommend users using modern CMAKE_*_OUTPUT_DIRECTORY variables to
configure paths.

Prioritize legacy variables only if set by the user. Removes
setting legacy CMake variable such as EXECUTE_OUTPUT_PATH and
LIBRARY_OUTPUT_PATH as cache variables. Add support for
modern CMAKE_*_OUTPUT_DIRECTORY variables, if they are set by the
user.

Author: blowekamp

CMakeLists.txt

@@ -118,20 +118,39 @@ if(BUILD_SHARED_LIBS)
 endif()
 
 #-----------------------------------------------------------------------------
-if(NOT EXECUTABLE_OUTPUT_PATH)
-  set(EXECUTABLE_OUTPUT_PATH ${GDCM_BINARY_DIR}/bin CACHE PATH "Single output directory for building all executables.")
-  mark_as_advanced(EXECUTABLE_OUTPUT_PATH)
+# Compatibility with older usage of EXECUTABLE_OUTPUT_PATH and LIBRARY_OUTPUT_PATH.
+# This should be removed in the future.
+if(EXECUTABLE_OUTPUT_PATH)
+  set(CMAKE_RUNTIME_OUTPUT_DIRECTORY ${EXECUTABLE_OUTPUT_PATH})
+  message(WARNING "EXECUTABLE_OUTPUT_PATH is deprecated. Use CMAKE_RUNTIME_OUTPUT_DIRECTORY instead.")
 endif()
-if(NOT LIBRARY_OUTPUT_PATH)
-  set(LIBRARY_OUTPUT_PATH ${GDCM_BINARY_DIR}/bin CACHE PATH "Single output directory for building all libraries.")
-  mark_as_advanced(LIBRARY_OUTPUT_PATH)
+if(LIBRARY_OUTPUT_PATH)
+  set(CMAKE_LIBRARY_OUTPUT_DIRECTORY ${LIBRARY_OUTPUT_PATH})
+  set(CMAKE_ARCHIVE_OUTPUT_DIRECTORY ${LIBRARY_OUTPUT_PATH})
+  message(WARNING "LIBRARY_OUTPUT_PATH is deprecated. Use CMAKE_LIBRARY_OUTPUT_DIRECTORY and CMAKE_ARCHIVE_OUTPUT_DIRECTORY instead.")
 endif()
 
-# TODO: The following should be used for CMake 3 and beyond,
-# EXECUTABLE_OUTPUT_PATH and LIBRARY_OUTPUT_PATH are deprecated
-set(CMAKE_RUNTIME_OUTPUT_DIRECTORY ${EXECUTABLE_OUTPUT_PATH})
-set(CMAKE_ARCHIVE_OUTPUT_DIRECTORY ${LIBRARY_OUTPUT_PATH})
-set(CMAKE_LIBRARY_OUTPUT_DIRECTORY ${LIBRARY_OUTPUT_PATH})
+if(NOT CMAKE_RUNTIME_OUTPUT_DIRECTORY)
+  set(CMAKE_RUNTIME_OUTPUT_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}/bin)
+endif()
+if(NOT CMAKE_LIBRARY_OUTPUT_DIRECTORY)
+  set(CMAKE_LIBRARY_OUTPUT_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}/bin)
+endif()
+if(NOT CMAKE_ARCHIVE_OUTPUT_DIRECTORY)
+  set(CMAKE_ARCHIVE_OUTPUT_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}/bin)
+endif()
+
+# Set for legacy internal usage of EXECUTABLE_OUTPUT_PATH and LIBRARY_OUTPUT_PATH
+if (NOT EXECUTABLE_OUTPUT_PATH)
+  set(EXECUTABLE_OUTPUT_PATH ${CMAKE_RUNTIME_OUTPUT_DIRECTORY})
+endif()
+if (NOT LIBRARY_OUTPUT_PATH)
+  if (BUILD_SHARED_LIBS)
+    set(LIBRARY_OUTPUT_PATH ${CMAKE_LIBRARY_OUTPUT_DIRECTORY})
+  else()
+    set(LIBRARY_OUTPUT_PATH ${CMAKE_ARCHIVE_OUTPUT_DIRECTORY})
+  endif()
+endif()
 
 #-----------------------------------------------------------------------------
 # Adding GDCM_DATA_ROOT