message: look for clang versions not just generic version
diff: # Note: clang 3.6 won't compile MLDB if GCC6 is installed
  -CLANGXX?=clang++
  -CLANG?=clang
  +find_command=$(foreach command,$(firstword $(1)),$(if $(shell which $(command)),$(command),$(call find_command,$(wordlist 2,10000,$(1)))))
  +
  +CLANGXX?=$(call find_command,clang++ clang++-13 clang++-12 clang++-11 clang++-10 clang++-9 clang++-8)
  +CLANG?=$(call find_command,clang clang-13 clang-12 clang-11 clang-10 clang-9 clang-8)
  CLANG_VERSION:=$(shell $(CLANGXX) --version | head -n1 | awk '{ print $4; }' | sed 's/-*//g')
  CXX_VERSION?=$(CLANG_VERSION)
  