toolchain: introduce HOST_DIR option

Allow the user to define HOST_DIR in the config menu.

This way when building an internal toolchain a separate (maybe shared)
output directory may be defined and the toolchain can be used by
multiple users and/or projects.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Acked-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>
diff --git a/Makefile b/Makefile
index 9563740..914d2ed 100644
--- a/Makefile
+++ b/Makefile
@@ -274,8 +274,8 @@
 
 GNU_TARGET_SUFFIX:=-$(call qstrip,$(BR2_GNU_TARGET_SUFFIX))
 
-# packages compiled for the host goes here
-HOST_DIR:=$(BASE_DIR)/host
+# packages compiled for the host go here
+HOST_DIR:=$(call qstrip,$(BR2_HOST_DIR))
 
 # stamp (dependency) files go here
 STAMP_DIR:=$(BASE_DIR)/stamps