Perform Boost environment variables check after call to common superbuild

This check uses the USE_SYSTEM_boost CMake variable, automatically set by common-superbuild.
To use it, this check must be performed after call to common-superbuild, or it throws an error.

CMakeLists.txt

@@ -203,13 +203,6 @@ set(boost_libraries
 set(boost_extra_options
   "-sNO_BZIP2=1")
 
-# Check if some Boost environment variables could hide local Boost install
-if (NOT ${USE_SYSTEM_boost} AND (DEFINED ENV{BOOSTROOT} OR DEFINED ENV{BOOST_ROOT} OR DEFINED ENV{BOOST_LIBRARYDIR} OR DEFINED ENV{BOOST_INCLUDEDIR}))
-  message(WARNING "Some Boost environment variables are set and may hide the local superbuild Boost installation. "
-                  "Consider enabling USE_SYSTEM_boost flag or unsetting the following environement variables :\n"
-                  " BOOSTROOT=$ENV{BOOSTROOT}\n BOOST_ROOT=$ENV{BOOST_ROOT}\n BOOST_LIBRARYDIR=$ENV{BOOST_LIBRARYDIR}\n BOOST_INCLUDEDIR=$ENV{BOOST_INCLUDEDIR}")
-endif()
-
 list(APPEND superbuild_version_files
   "${CMAKE_CURRENT_LIST_DIR}/versions.cmake")
 list(APPEND superbuild_project_roots
@@ -236,3 +229,10 @@ if (ENABLE_slam AND ENABLE_old_slam)
 endif(ENABLE_slam AND ENABLE_old_slam)
 
 add_subdirectory(common-superbuild)
+
+# Check if some Boost environment variables could hide local Boost install
+if (NOT ${USE_SYSTEM_boost} AND (DEFINED ENV{BOOSTROOT} OR DEFINED ENV{BOOST_ROOT} OR DEFINED ENV{BOOST_LIBRARYDIR} OR DEFINED ENV{BOOST_INCLUDEDIR}))
+  message(WARNING "Some Boost environment variables are set and may hide the local superbuild Boost installation. "
+                  "Consider enabling USE_SYSTEM_boost flag or unsetting the following environement variables :\n"
+                  " BOOSTROOT=$ENV{BOOSTROOT}\n BOOST_ROOT=$ENV{BOOST_ROOT}\n BOOST_LIBRARYDIR=$ENV{BOOST_LIBRARYDIR}\n BOOST_INCLUDEDIR=$ENV{BOOST_INCLUDEDIR}")
+endif()
\ No newline at end of file