Makefile: clang on mac

[kazuf3]

Simply clang and clang++ works for me rather than clang-${LLVM_VERSION} which gives me:

$ make
clang-6.0 -O3 -std=c++11 -Wall -fno-use-cxa-atexit -fPIC -c vb.cpp -o vb.o
make: clang-6.0: No such file or directory
make: *** [vb.o] Error 1

so,

  CLANG ?= clang

and

  CLANG ?= clang++

[radujica]

+1 This would also simplify the Python installation scripts AND remove the need to link between clang's (as mentioned in docs and found in practice).