Recompiling mex file: Error using mex clang: error: unsupported option '-fopenmp'

I am trying to compile a mex file with the following commands:

% minFunc
fprintf('Compiling minFunc files...\n');
mex -outdir minFunc/compiled minFunc/mex/mcholC.c
mex -outdir minFunc/compiled minFunc/mex/lbfgsC.c
mex -outdir minFunc/compiled minFunc/mex/lbfgsAddC.c
% mex -outdir minFunc/compiled CXX='g++' CXXFLAGS='\$CXXFLAGS -O3 -funroll-loops -fopenmp' LDFLAGS="\$LDFLAGS -fopenmp" minFunc/mex/lbfgsProdC.cpp
mex -v -outdir minFunc/compiled CXX='g++' CXXFLAGS='\$CXXFLAGS -O3 -fopenmp' LDFLAGS="\$LDFLAGS -fopenmp" CXXOPTIMFLAGS='-O3' minFunc/mex/lbfgsProdC.cpp

% mex -v -outdir minFunc/compiled -fopenmp -O3 minFunc/mex/lbfgsProdC.cpp
% mex -v -outdir minFunc/compiled CXX='g++' CXXFLAGS='\$CXXFLAGS -O3 -msse4 -ftree-vectorize -ftree-vectorizer-verbose=5 -ftree-loop-distribution -funroll-all-loops -ftracer -funroll-loops -fopenmp' LDFLAGS="\$LDFLAGS -fopenmp" minFunc/mex/lbfgsProdC.cpp
% mex -outdir minFunc/compiled CXX='g++' CFLAGS='\$CFLAGS -O3 -msse4 -ftree-vectorize -ftree-vectorizer-verbose=5 -ftree-loop-distribution -funroll-all-loops -ftracer -funroll-loops -fopenmp' LDFLAGS="\$LDFLAGS -fopenmp" minFunc/mex/lbfgsProdC.c
mex -v -outdir minFunc/compiled COMPFLAGS="-DUSE_WINDOWS /openmp /O3 $COMPFLAGS"  minFunc/mex/lbfgsProdC.cpp

And I get the following error message:

Error using mex clang: error: unsupported option '-fopenmp'

Error in mexAll (line 7)
mex -v -outdir minFunc/compiled CXX='g++' CXXFLAGS='\$CXXFLAGS -O3 -fopenmp' LDFLAGS="\$LDFLAGS -fopenmp" CXXOPTIMFLAGS='-O3'
minFunc/mex/lbfgsProdC.cpp 
The code was running fine on Matlab R2016a, but now that I have upgraded to R2017a, my programm runs crashes. I the tried to recompile the mex file and got the error. Also, it might be worth mentioning that I have updated my OS to High Sierra.