bdwgc: fix static build

Fixes:
http://autobuild.buildroot.net/results/6d3/6d3f73f7b5e4e7bd1293aae9b626f38ac456b6c4/
http://autobuild.buildroot.net/results/1ba/1ba511c629f724eee8b75b9b34fe8db154b3cfe1/
http://autobuild.buildroot.net/results/a54/a54cc1bdc5dcb4c459cfbcae3368811e2170d100/

and more.

Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/bdwgc/bdwgc.mk

@@ -18,8 +18,13 @@ BDWGC_DEPENDENCIES = libatomic_ops host-pkgconf
 # solution.
 BDWGC_AUTORECONF = YES
 
+BDWGC_CFLAGS = $(TARGET_CFLAGS)
+ifeq ($(BR2_STATIC_LIBS),y)
+BDWGC_CFLAGS += -DGC_NO_DLOPEN
+endif
+
 # Ensure we use the system libatomic_ops, and not the internal one.
-BDWGC_CONF_OPTS = --with-libatomic-ops=yes
+BDWGC_CONF_OPTS = --with-libatomic-ops=yes CFLAGS="$(BDWGC_CFLAGS)"
 HOST_BDWGC_CONF_OPTS = --with-libatomic-ops=yes
 
 $(eval $(autotools-package))