libs/expat: Fix poor entropy compilation error

Add the same workaround as for the expat package in toolchain.
I'm not really sure what made it work for me earlier but this seems to fix it.

Signed-off-by: Daniel Engberg <daniel.engberg.lists@pyret.net>

libs/expat/Makefile

@@ -39,6 +39,9 @@ endef
 
 TARGET_CFLAGS += $(FPIC)
 
+HOST_CONFIGURE_VARS += \
+	CPPFLAGS="$(HOST_CFLAGS) -DXML_POOR_ENTROPY"
+
 CONFIGURE_ARGS += \
 	--enable-shared \
 	--enable-static