[gcc(refs/users/marxin/heads/PR94330-detect-missing-jobserver)] Provide warning for missing jobserver.

[Martin Liska]

https://gcc.gnu.org/g:d572544c13c01e739d4d1dd5e5641cc636404a53

commit d572544c13c01e739d4d1dd5e5641cc636404a53
Author: Martin Liska <mliska@suse.cz>
Date:   Thu Mar 26 09:57:35 2020 +0100

    Provide warning for missing jobserver.
    
    gcc/ChangeLog:
    
    2020-03-26  Martin Liska  <mliska@suse.cz>
    
            PR driver/94330
            * lto-wrapper.c (run_gcc): When using -flto=jobserver,
            report warning when the jobserver is not detected.

Diff:
---
 gcc/lto-wrapper.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/gcc/lto-wrapper.c b/gcc/lto-wrapper.c
index 46a88b233f6..6263c164888 100644
--- a/gcc/lto-wrapper.c
+++ b/gcc/lto-wrapper.c
@@ -1473,10 +1473,16 @@ run_gcc (unsigned argc, char *argv[])
       auto_parallel = 0;
       parallel = 0;
     }
-  else if (!jobserver && jobserver_active_p ())
+  else
     {
-      parallel = 1;
-      jobserver = 1;
+      bool active_jobserver = jobserver_active_p ();
+      if (jobserver && !active_jobserver)
+	warning (0, "jobserver is not available.");
+      else if (!jobserver && active_jobserver)
+	{
+	  parallel = 1;
+	  jobserver = 1;
+	}
     }
 
   if (linker_output)