[Makefile] Set cmake variable BUILD_TESTING.

  This cmake variable is planned to replace variable DISABLE_TESTS defined
  in the cmake submodule.

doc/Makefile

@@ -20,11 +20,13 @@ HUMANOID=TRUE
 
 BUILD_TYPE=Release
 DISABLE_TESTS=OFF
+BUILD_TESTING=ON
 ifeq (${BUILD_TYPE},Debug)
   BUILD_FOLDER=build
 else
   BUILD_FOLDER=build-rel
   DISABLE_TESTS=ON
+  BUILD_TESTING=OFF
 endif
 
 OSG_PACKAGE=osg-dae
@@ -54,7 +56,8 @@ hpp-template-corba_repository=${HPP_REPO}
 
 # Either a version tag (e.g. v4.3.0), master or devel
 HPP_VERSION=devel
-HPP_EXTRA_FLAGS=-DDISABLE_TESTS=${DISABLE_TESTS}
+HPP_EXTRA_FLAGS=-DDISABLE_TESTS=${DISABLE_TESTS} \
+	-DBUILD_TESTING=${BUILD_TESTING}$
 
 hpp-util_branch=${HPP_VERSION}
 hpp-util_repository=${HPP_REPO}