Disable -Werror when building qemu

When building the system versions of qemu, there are some warnings
which terminate the build if this flag is used. Disable it until qemu
upstream fixes the problem.

Signed-off-by: Keith Packard <keithp@keithp.com>

Author: keith-packard

Makefile.in

@@ -861,7 +861,8 @@ stamps/build-qemu: $(QEMU_SRCDIR) $(QEMU_SRC_GIT)
 		--prefix=$(INSTALL_DIR) \
 		--target-list=$(QEMU_TARGETS) \
 		--interp-prefix=$(INSTALL_DIR)/sysroot \
-		--python=python3
+		--python=python3 \
+		--disable-werror
 	$(MAKE) -C $(notdir $@)
 	$(MAKE) -C $(notdir $@) install
 	mkdir -p $(dir $@)