Ensure Out of Source builds

In source builds creates a lot of noise on the source tree,
creating tons of temporaries that makes git status cry, and it also
creates dangerous files that have names similar to actual source
and could make a developer use them by mistake.

Make out of source buiild mandatory to remove that, it also makes
CMake code easier to read.

Signed-off-by: Tomaz Canabrava <tomaz.canabrava@intel.com>

CMakeLists.txt

@@ -3,10 +3,13 @@
 project(Subsurface)
 cmake_minimum_required(VERSION 2.8.11)
 
-
 # global settings
 
 set(CMAKE_AUTOMOC ON)
+include(cmake/Modules/MacroOutOfSourceBuild.cmake)
+MACRO_ENSURE_OUT_OF_SOURCE_BUILD(
+    "We don't support building in source, please create a build folder elsewhere and remember to run git clean -xdf to remoev temporary files created by CMake."
+)
 
 option(LIBGIT2_FROM_PKGCONFIG "use pkg-config to retrieve libgit2" OFF)
 option(LIBDC_FROM_PKGCONFIG "use pkg-config to retrieve libdivecomputer" OFF)
@@ -153,18 +156,7 @@ endif()
 
 set(SUBSURFACE_LINK_LIBRARIES ${SUBSURFACE_LINK_LIBRARIES} ${LIBDIVECOMPUTER_LIBRARIES} ${LIBGIT2_LIBRARIES} ${LIBUSB_LIBRARIES})
 
-# handle out of tree build correctly
-string(COMPARE EQUAL "${${PROJECT_NAME}_SOURCE_DIR}" "${${PROJECT_NAME}_BINARY_DIR}" insource)
-if (insource)
-	message(STATUS "building in Subsurface source tree - we recommend out of tree builds")
-else()
-	message(STATUS "out of source build from source in ${${PROJECT_NAME}_SOURCE_DIR}")
-endif()
-get_filename_component(PARENTDIR ${${PROJECT_NAME}_SOURCE_DIR} PATH)
-string(COMPARE EQUAL "${${PROJECT_NAME}_SOURCE_DIR}" "${PARENTDIR}" insourcesubdir)
-if(NOT (insource OR insourcedir))
-	add_custom_target(link_marble_data ALL COMMAND rm -rf ./marbledata && ln -s ${CMAKE_SOURCE_DIR}/marbledata ${CMAKE_BINARY_DIR}/marbledata)
-endif()
+add_custom_target(link_marble_data ALL COMMAND rm -rf ./marbledata && ln -s ${CMAKE_SOURCE_DIR}/marbledata ${CMAKE_BINARY_DIR}/marbledata)
 
 # configure Qt.
 if(SUBSURFACE_MOBILE)