Automatically detect GNU jobserver with -flto.

2019-08-13  Martin Liska  <mliska@suse.cz>

	* doc/invoke.texi: Document automatic detection of jobserver.
	* lto-wrapper.c (run_gcc): Detect jobserver always.

From-SVN: r274329

gcc/ChangeLog

+2019-08-13  Martin Liska  <mliska@suse.cz>
+
+	* doc/invoke.texi: Document automatic detection of jobserver.
+	* lto-wrapper.c (run_gcc): Detect jobserver always.
+
 2019-08-13  Uroš Bizjak  <ubizjak@gmail.com>
 
 	* config/i386/i386.md (ix86_expand_vector_set) <case E_V2SImode>:

gcc/doc/invoke.texi

@@ -10422,7 +10422,8 @@ job server mode to determine the number of parallel jobs. This
 is useful when the Makefile calling GCC is already executing in parallel.
 You must prepend a @samp{+} to the command recipe in the parent Makefile
 for this to work.  This option likely only works if @env{MAKE} is
-GNU make.
+GNU make.  Even without the option value, GCC tries to automatically
+detect a running GNU make's job server.
 
 Use @option{-flto=auto} to use GNU make's job server, if available,
 or otherwise fall back to autodetection of the number of CPU threads

gcc/lto-wrapper.c

@@ -1423,7 +1423,7 @@ run_gcc (unsigned argc, char *argv[])
       auto_parallel = 0;
       parallel = 0;
     }
-  else if (!jobserver && auto_parallel)
+  else if (!jobserver)
     jobserver = jobserver_active_p ();
 
   if (linker_output)