Using GNU make jobserver from GCC

[Jan Hubicka]

Hello,
GCC LTO implementation has ability to execute multiple parallel compilations 
(see -flto switch documentation).
This is implemented by streaming out several object files, producing a makefile 
and then executing
sub-make command. -flto=n makes GCC to pass -j=n to the submake, while 
-flto=jobserv makes GCC to pass
-j=jobserv to the submake.

Now there are two problems, first is that GCC also parallelize its streaming 
phase internally (not via make)
and in this case -flto=jobserv is ignored, because GCC does not know how to 
communicate with the Make's
jobserver.  Other problem is that -flto=jobserv requires changes to Makefile 
where "+" needs to be added
so proper variables are passed.

I wonder if thre can be any additional support from GNU's make to make "+" 
unnecesary and if it would
be possible to spearate client side of GNU Make's jobserver into separate file 
that can be spossibly
shared in between GNU make and GCC - perhaps via liberty library?

Thanks,
Honza