make[1]: warning: jobserver unavailable: using -j1. Add `+' to parent make rule.

[Peng Yu]

Hi,

I get the warning as shown in the subject when I use 'make -j<number>'
(the warning doesn't show if I use 'make -j'). I am not able to create
a standalone test case, because my Makefile uses some customized make
library. But could anybody give me some hint on what may cause this
problem? Thanks.

-- 
Regards,
Peng