elftosb: use HOST_CONFIGURE_OPTS instead of HOST_MAKE_ENV

HOST_CONFIGURE_OPTS allows to pass the correct CC, CXX, CFLAGS,
CXXFLAGS, etc. For example, it allows the elftosb build process to
properly use ccache when available.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/elftosb/elftosb.mk

@@ -8,7 +8,7 @@ ELFTOSB_SOURCE = elftosb-$(ELFTOSB_VERSION).tar.gz
 ELFTOSB_SITE = http://repository.timesys.com/buildsources/e/elftosb/elftosb-$(ELFTOSB_VERSION)
 
 define HOST_ELFTOSB_BUILD_CMDS
-	$(HOST_MAKE_ENV) $(MAKE) -C $(@D) all
+	$(HOST_CONFIGURE_OPTS) $(MAKE) -C $(@D) all
 endef
 
 define HOST_ELFTOSB_INSTALL_CMDS