fixed CMAKE_OPTIONS_COMMON variable references (#467)

added CMAKE_OPTIONS_EXTRA

contrib/docker/Makefile

@@ -26,11 +26,16 @@ GIT_COMMIT = $(shell git rev-parse HEAD)
 DBUILD_VERSION = ${GIT_COMMIT}_${PYTHON_VERSION}
 DBUILD_DIR = ${DIR}/contrib/docker/.build-${DBUILD_VERSION}
 
+# Enable additional options to be added on the command line
+ifndef CMAKE_OPTIONS_EXTRA
+    CMAKE_OPTIONS_EXTRA = ""
+endif
+
 # For gcc builds, we do NOT regard warnings as errors
 # For clang builds, we DO make warnings into errors
-CMAKE_OPTIONS_COMMON=-DNGRAPH_BUILD_DOXYGEN_DOCS=ON -DNGRAPH_BUILD_SPHINX_DOCS=ON -DCMAKE_BUILD_TYPE=RelWithDebInfo
-CMAKE_OPTIONS_GCC=$CMAKE_OPTIONS_COMMON -DNGRAPH_INSTALL_PREFIX=${DOCKUSER_HOME}/ngraph-cpp-test/BUILD-GCC/ngraph_dist -DNGRAPH_USE_PREBUILT_LLVM=TRUE
-CMAKE_OPTIONS_CLANG=$CMAKE_OPTIONS_COMMON -DNGRAPH_INSTALL_PREFIX=${DOCKUSER_HOME}/ngraph-cpp-test/BUILD-CLANG/ngraph_dist -DCMAKE_CXX_COMPILER=clang++-3.9 -DCMAKE_C_COMPILER=clang-3.9 -DNGRAPH_WARNINGS_AS_ERRORS=ON -DNGRAPH_USE_PREBUILT_LLVM=TRUE
+CMAKE_OPTIONS_COMMON=-DNGRAPH_BUILD_DOXYGEN_DOCS=ON -DNGRAPH_BUILD_SPHINX_DOCS=ON -DCMAKE_BUILD_TYPE=RelWithDebInfo $(CMAKE_OPTIONS_EXTRA)
+CMAKE_OPTIONS_GCC=$(CMAKE_OPTIONS_COMMON) -DNGRAPH_INSTALL_PREFIX=${DOCKUSER_HOME}/ngraph-cpp-test/BUILD-GCC/ngraph_dist -DNGRAPH_USE_PREBUILT_LLVM=TRUE
+CMAKE_OPTIONS_CLANG=$(MAKE_OPTIONS_COMMON)-DNGRAPH_INSTALL_PREFIX=${DOCKUSER_HOME}/ngraph-cpp-test/BUILD-CLANG/ngraph_dist -DCMAKE_CXX_COMPILER=clang++-3.9 -DCMAKE_C_COMPILER=clang-3.9 -DNGRAPH_WARNINGS_AS_ERRORS=ON -DNGRAPH_USE_PREBUILT_LLVM=TRUE
 
 CALLER_UID := $(shell id -u)
 CALLER_GID := $(shell id -g)