automake: use whenever possible the ACLOCAL_HOST_DIR variable

Use the ACLOCAL_HOST_DIR in the GTK_DOC_M4_INSTALL hook.

Move the ACLOCAL_HOST_DIR definition at the beginning so the definition
is ahead the utilization.

Signed-off-by: Fabio Porcedda <fabio.porcedda@gmail.com>
Cc: Romain Naour <romain.naour@openwide.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/automake/automake.mk

@@ -12,8 +12,11 @@ AUTOMAKE_LICENSE_FILES = COPYING
 
 HOST_AUTOMAKE_DEPENDENCIES = host-autoconf
 
+ACLOCAL_HOST_DIR = $(HOST_DIR)/usr/share/aclocal
+
 define GTK_DOC_M4_INSTALL
-	$(INSTALL) -D -m 0644 package/automake/gtk-doc.m4 $(HOST_DIR)/usr/share/aclocal/gtk-doc.m4
+	$(INSTALL) -D -m 0644 package/automake/gtk-doc.m4 \
+		$(ACLOCAL_HOST_DIR)/gtk-doc.m4
 endef
 
 # ensure staging aclocal dir exists
@@ -29,5 +32,4 @@ $(eval $(host-autotools-package))
 # variables used by other packages
 AUTOMAKE = $(HOST_DIR)/usr/bin/automake
 ACLOCAL_DIR = $(STAGING_DIR)/usr/share/aclocal
-ACLOCAL_HOST_DIR = $(HOST_DIR)/usr/share/aclocal
 ACLOCAL = $(HOST_DIR)/usr/bin/aclocal -I $(ACLOCAL_DIR)