package/collectd: work around gcc bug 68485

collectd is impacted by the microblaze-specific gcc bug #68485 [0].

As for all other impacted packages, force no optimisation when using a
toolchain riddled with that bug.

Fixes:
   http://autobuild.buildroot.net/results/6a8/6a87bbe17e6f606a97097800dc484a7b17bffa7d/

[0] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68485

Signed-off-by: Giulio Benetti <giulio.benetti@benettiengineering.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

package/collectd/collectd.mk

@@ -27,6 +27,14 @@ COLLECTD_PLUGINS_DISABLE = \
 
 COLLECTD_CONF_ENV += LIBS="-lm"
 
+COLLECTD_CFLAGS = $(TARGET_CFLAGS)
+
+ifeq ($(BR2_TOOLCHAIN_HAS_GCC_BUG_68485),y)
+COLLECTD_CFLAGS += -O0
+endif
+
+COLLECTD_CONF_ENV += CFLAGS="$(COLLECTD_CFLAGS)"
+
 #
 # NOTE: There's also a third availible setting "intswap", which might
 # be needed on some old ARM hardware (see [2]), but is not being