[SeaBIOS] Patch for warning in Makefile for seabios 1.7.0

[wuodan at hispeed.ch]

Hello

I tripped over a warning in v1.7.0, which did not occur when building v1.6.3.

The warning occurs when building parallel, for example "make -j3 defconfig".
Here is the warning:
make[1]:warning: jobserver unavailable: using -j1.  Add `+' to parent make rule.

I don't know if it is relevant, but I tried to patch it, diff is at end of this mail.
This came out of a feature request in Gentoo:
=> https://bugs.gentoo.org/show_bug.cgi?id=415665

Regards
Stefan Kuhn

Here's the diff:
diff orig/seabios-1.7.0/Makefile work/seabios-1.7.0/Makefile 
237c237
< $(Q)$(MAKE) -C $(OUT) -f $(CURDIR)/tools/kconfig/Makefile srctree=$(CURDIR) src=tools/kconfig obj=tools/kconfig Q=$(Q) Kconfig=$(CURDIR)/src/Kconfig $1
---
> $(Q)+$(MAKE) -C $(OUT) -f $(CURDIR)/tools/kconfig/Makefile srctree=$(CURDIR) src=tools/kconfig obj=tools/kconfig Q=$(Q) Kconfig=$(CURDIR)/src/Kconfig $1