make spec

Using /usr/bin/llvm-config [version=5.0.0]
./bin/crystal build  -o .build/all_spec spec/all_spec.cr
Using compiled compiler at `.build/crystal'
Error in spec/all_spec.cr:1: while requiring "prelude"

require "spec"
^

in src/prelude.cr:15: while requiring "exception"

require "exception"
^

in src/exception.cr:1: while requiring "callstack"

require "callstack"
^

in src/callstack.cr:1: while requiring "c/dlfcn": can't find file 'c/dlfcn' relative to '/home/edoardo/crystal/src'

require "c/dlfcn"
^

make: *** [Makefile:106: .build/all_spec] Error 1