Include config_build.mk unconditionally

I hope this will unbreak cross-compilation after
162a4f8d. Otherwise I see stuff being built
for the BUILD platform with the HOST compiler.

Change-Id: I4f34a29bb1bfd9345610255bf5bb917a87c8c6f2

cross_tail_build/Makefile

@@ -26,9 +26,7 @@
 #
 #*************************************************************************
 
-ifeq ($(strip $(SOLARENV)),)
 include $(dir $(realpath $(firstword $(MAKEFILE_LIST))))/../config_build.mk
-endif
 
 export gb_Side=build