ola: fix compilation with GCC4

The configure script confusingly sets CXXFLAGS to gnu++11 but does
not use that to check the important stuff. Fix that.

Signed-off-by: Rosen Penev <rosenp@gmail.com>

net/ola/Makefile

@@ -65,6 +65,9 @@ HOST_CONFIGURE_ARGS += \
 	--disable-doxygen-html \
 	--disable-doxygen-doc
 
+HOST_CPPFLAGS += \
+	-std=gnu++11
+
 HOST_LDFLAGS += -Wl,-rpath="$(STAGING_DIR_HOSTPKG)/lib"
 TARGET_LDFLAGS += $(if $(CONFIG_USE_GLIBC),-lm)