Makefile check for clang

[Ganesh Kathiresan]

Hi, I noticed make failed if clang is not present, can we add a check like this:

CHECK := $(shell which clang)

ifeq ($(CHECK),)
$(warning no clang found, consider apt-get install clang, using gcc now)
CC = gcc
else
$(info using clang over gcc)
CC = clang
endif

[mkirchner]

Hi @ganesh-k13 , absolutely! Would you be able to suggest the change in a PR?