add validation for when the command buffer before the response file gets truncated

Same change, new PR...

>While playing with a new toolchain I noticed that my command line got truncated. Finally I found out that it was the command before the respone file suffix that was too big for the current command_buf length.

>I added a validation for it along what should be a clear message of what's happening and what to do about it and I stop the execution instead of letting it continue with a truncated command that won't probably work as expected (if at all).