uboot-mvebu: fix build on hosts lacking pkg-config

The uboot-mvebu package incorrectly used the host pkg-config for the tool
build parts, which broke the build on systems lacking pkg-config and only
worked by accident on those that have it installed.

Export the host-build specific environment variables for the uboot build
to redirect pkg-config invocations to our staged host build pkg-config in
buildroot.

Signed-off-by: Jo-Philipp Wich <jo@mein.io>

package/boot/uboot-mvebu/Makefile

@@ -15,6 +15,7 @@ PKG_HASH:=7e7477534409d5368eb1371ffde6820f0f79780a1a1f676161c48442cb303dfd
 
 include $(INCLUDE_DIR)/u-boot.mk
 include $(INCLUDE_DIR)/package.mk
+include $(INCLUDE_DIR)/host-build.mk
 
 define U-Boot/Default
   BUILD_TARGET:=mvebu
@@ -31,6 +32,8 @@ endef
 UBOOT_TARGETS:= \
 	clearfog
 
+Build/Exports:=$(Host/Exports)
+
 define Build/Configure
 	# enable additional options beyond clearfog_defconfig
 	echo CONFIG_NET_RANDOM_ETHADDR=y >> $(PKG_BUILD_DIR)/configs/$(BUILD_VARIANT)_defconfig