Don't prompt user when killing Flymake processes

* lisp/progmodes/flymake.el (flymake-start-syntax-check-process):
Don’t prompt the user when killing Flymake processes.

* doc/misc/flymake.texi (Starting the syntax check process):
Document new behavior.

doc/misc/flymake.texi

@@ -697,7 +697,8 @@ The command line (command name and the list of arguments) for launching a proces
 initialization function.  Flymake then just calls @code{start-process}
 to start an asynchronous process and configures a process filter and
 sentinel, which are used for processing the output of the syntax check
-tool.
+tool.  When exiting Emacs, running Flymake processes will be killed
+without prompting the user.
 
 @node Parsing the output
 @section Parsing the output

etc/NEWS

@@ -478,6 +478,12 @@ This is done with the help of 'c-or-c++-mode' function which analyses
 contents of the buffer to determine whether it's a C or C++ source
 file.
 
+** Flymake
+
++++
+*** Emacs does no longer prompt the user before killing Flymake
+processes on exit.
+
 
 * New Modes and Packages in Emacs 26.1
 

lisp/progmodes/flymake.el

@@ -1072,6 +1072,7 @@ For the format of LINE-ERR-INFO, see `flymake-ler-make-ler'."
                        "flymake-proc" (current-buffer) cmd args))))
         (set-process-sentinel process 'flymake-process-sentinel)
         (set-process-filter process 'flymake-process-filter)
+        (set-process-query-on-exit-flag process nil)
         (push process flymake-processes)
 
         (setq flymake-is-running t)