When SHELL_NO_ECHO was defined and not SHELL_NO_PROMPT build was broken because _putchar was not defined. This define _putchar when one of SHELL_NO_PROMPT or SHELL_NO_ECHO is not defined.
When SHELL_NO_ECHO was defined and not SHELL_NO_PROMPT build was broken because _putchar was not defined. This define _putchar when one of SHELL_NO_PROMPT or SHELL_NO_ECHO is not defined.