Patch merged into coreboot/master: e9b7e25 util/xcompile/xcompile: Allow to override `HOSTCC` variable

the following patch was just integrated into master:
commit e9b7e25708db1eb234c87def87a8e4e9b5c03b28
Author: Paul Menzel 
Date:   Thu Apr 9 18:15:09 2015 +0200

util/xcompile/xcompile: Allow to override `HOSTCC` variable

Currently `xcompile` generates `.xcompile` with the following at the
    top.

# platform agnostic and host tools
    	IASL:=iasl
    	HOSTCC:=gcc

The assignment `:=` doesn’t allow to override the variable. So use `?=`
    instead so the host compiler can be passed to coreboot.

HOSTCC=gcc-5 make

Note, that this is just a hack, as the existence of `gcc` is checked
    beforehand.

Change-Id: Iebf3e43eb7eaffa7cf0efe97710d9feb3fe2a989
    Signed-off-by: Paul Menzel 
    Reviewed-on: http://review.coreboot.org/9457
    Tested-by: build bot (Jenkins)
    Reviewed-by: Patrick Georgi

See http://review.coreboot.org/9457 for details.

-gerrit