Help: document exit code of command cmake(1)

Help/manual/cmake.1.rst

@@ -1059,6 +1059,17 @@ To view the presets available for a project, use
 
   cmake <source-dir> --list-presets
 
+
+.. _`CMake Exit Code`:
+
+Return Value (Exit Code)
+========================
+
+Upon regular termination, the **cmake** executable returns the exit code 0.
+If termination is caused by the command :command:`message(FATAL_ERROR)`,
+then a non-zero exit code is returned.
+
+
 See Also
 ========