make mpi optional in makefile

Makefile

@@ -67,11 +67,12 @@ endif
 # The mpic++ wrapper only adds MPI specific flags to the g++ command line.
 # The actual compiler/linker flags added can be viewed by running 'mpic++ --showme:compile' and 'mpic++ --showme:link'
 CXX = mpic++
+HAS_MPI = 1
 
 SOURCEDIR:= Source
 INCLUDEPATH:= $(addprefix $(SOURCEDIR)/, Common/Include CNTKv2LibraryDll CNTKv2LibraryDll/API Math CNTK ActionsLib ComputationNetworkLib SGDLib SequenceTrainingLib CNTK/BrainScript Readers/ReaderLib)
 # COMMON_FLAGS include settings that are passed both to NVCC and C++ compilers.
-COMMON_FLAGS:= -DHAS_OPENMPI=0 -D_POSIX_SOURCE -D_XOPEN_SOURCE=600 -D__USE_XOPEN2K -std=c++11
+COMMON_FLAGS:= -DHAS_OPENMPI=$(HAS_MPI) -D_POSIX_SOURCE -D_XOPEN_SOURCE=600 -D__USE_XOPEN2K -std=c++11
 CPPFLAGS:= 
 CXXFLAGS:= -msse4.1 -mssse3 -std=c++0x -fopenmp -fpermissive -fPIC -Werror -fcheck-new
 LIBPATH:=