Passing jobserver file descriptors to all children

[R. Diez]

Hi all:

I am trying to use GCC's -flto=jobserver flag, but I cannot easily add the '+' character in front of the makefile recipe with 
Autoconf/Automake. See here for more details:

https://gcc.gnu.org/ml/gcc-help/2020-02/msg00069.html

The jobserver used to be a GNU Make-specific feature, but other things like GCC's LTO are starting to use it. GCC may use it during object 
file compilation in the future too, see this project:

https://gcc.gnu.org/wiki/ParallelGcc

In fact, any stage during a build process may be parallelised and start using the jobserver. With the advent of multicore CPUs, this will 
probably increase with time.

The requirement to prepend a '+' to the recipe or to use $(MAKE) then becomes a 
nuisance.

Is there a way to tell GNU Make to always pass those jobserver file descriptors 
to all children?

Thanks in advance,
  rdiez