Add a "make distclean" to src_configure for U-Boot.

sys-boot/u-boot/u-boot-9999.ebuild

 # Copyright (c) 2009 The Chromium OS Authors. All rights reserved.
 # Distributed under the terms of the GNU General Public License v2
 
 EAPI=2
 
 inherit cros-workon toolchain-funcs
 
 DESCRIPTION="Das U-Boot boot loader"
 HOMEPAGE="http://www.denx.de/wiki/U-Boot"
 LICENSE="GPL-2"
@@ skipping 10 matching lines @@
 #
 # Strip the ebuild directory to construct a valid CROS_WORKON_SUBDIR.  This can
 # be removed once all of the overlay make.confs specify CHROMEOS_U_BOOT without
 # the u-boot directory prefixed.
 #
 CROS_WORKON_SUBDIR="${u_boot#u-boot/}"
 
 src_configure() {
         elog "Using U-Boot config: ${config}"
 
+        emake distclean
         emake \
               ARCH=$(tc-arch-kernel) \
               CROSS_COMPILE="${CHOST}-" \
               USE_PRIVATE_LIBGCC=yes \
               ${config} || die "U-Boot configuration failed"
 }
 
 src_compile() {
         tc-getCC
         tc-getSTRIP
 
         emake \
               ARCH=$(tc-arch-kernel) \
               CROSS_COMPILE="${CHOST}-" \
               USE_PRIVATE_LIBGCC=yes \
               HOSTCC=${CC} \
               HOSTSTRIP=${STRIP} \
               all || die "U-Boot compile failed"
 }
 
 src_install() {
         dodir /u-boot
 
         insinto /u-boot
         doins u-boot.bin || die
 
         dobin "${S}"/tools/mkimage || die
 }