Subject: bug#45756: Always prepend '+' to the recipe line

From: "R. Diez" <[email-masked]>
Date: Wed, 13 Jan 2021 13:15:03 +0100

This is not just an issue while linking. Any stage, including compilation of a single object file, could use the GNU Make jobs server. So 
there should be a global option in Autoconf or Automake to prepend a '+' to all generated rules.

In fact, you would have thought that this should be the default, because any tool, at any stage, could decide in the future to go 
multithread, and there is no reason to ignore an existing GNU Make job server to limit the overall system load.

Beware that you cannot test this issue well with GCC at the moment, because GCC option -flto=jobserver will not issue any warning if the 
file descriptors are not available. I reported this a while ago, and it got fixed, but the target GCC version is 11, which has not been 
released yet:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94330