Show a better error message if cmake is missing

configure

@@ -27,6 +27,7 @@ exec echo "Either install python, or use cmake directly"
 
 import argparse
 import os
+import shutil
 import subprocess
 import sys
 import re
@@ -117,6 +118,11 @@ parser.add_argument('env', nargs='*', type=env_type, metavar='ENV_VAR=VALUE')
 
 args = parser.parse_args()
 
+if not shutil.which('cmake'):
+    print('CMake is required to proceed. Please install it via package manager,\n'
+          'or download the binary from https://cmake.org/')
+    sys.exit(1)
+
 cm_args = args.cm_args or []
 
 for env_key, env_value in args.env: