Update build_dll.py

Author: Adityakk9031

warp/_src/build_dll.py

@@ -190,6 +190,10 @@ def find_host_compiler() -> str:
                 os.environ[pair[0]] = pair[1]
 
         cl_path = shutil.which("cl.exe")
+        if not cl_path:
+            if verbose_cmd:
+                print("Warning: cl.exe not found in PATH after running vcvars64.bat")
+            return ""
         vc_tools_version = os.environ.get("VCToolsVersion", "")
         if not vc_tools_version:
             if verbose_cmd: