cdhit: add zlib dependency. (#13015)

* cdhit: add zlib dependency.

* Add zlib variant.

var/spack/repos/builtin/packages/cdhit/package.py

@@ -17,15 +17,19 @@ class Cdhit(MakefilePackage):
     version('4.6.8', 'bdd73ec0cceab6653aab7b31b57c5a8b')
 
     variant('openmp', default=True, description='Compile with multi-threading support')
+    variant('zlib', default=True, description='Compile with zlib')
 
     depends_on('perl', type=('build', 'run'))
+    depends_on('zlib', when='+zlib', type='link')
 
     def build(self, spec, prefix):
         mkdirp(prefix.bin)
+        make_args = []
         if '~openmp' in spec:
-            make('openmp=no')
-        else:
-            make()
+            make_args.append('openmp=no')
+        if '~zlib' in spec:
+            make_args.append('zlib=no')
+        make(*make_args)
 
     def setup_environment(self, spack_env, run_env):
         spack_env.set('PREFIX', prefix.bin)