kbuild: Fix 'make -j' problem

As pointed out by wli, all other compilation relies on fixdep to
exist already.

BTW, wli's benchmark numbers for the kallsyms speed-up patch:

-make -j bzImage  323.03s user 157.65s system  843% cpu 57.019 total
+make -j bzImage  270.02s user 147.01s system 1303% cpu 32.004 total

scripts/Makefile

@@ -15,4 +15,4 @@ build-targets := $(host-progs)
 subdir-	:= lxdialog kconfig
 
 # fixdep is needed to compile other host programs
-$(obj)/split-include $(obj)/docproc $(obj)/conmakehash: $(obj)/fixdep
+$(addprefix $(obj)/,$(filter-out fixdep,$(host-progs))): $(obj)/fixdep