prboom: fix static linking

Fixes:
http://autobuild.buildroot.net/results/97b/97bb50add010e44aca8fcb079d8df9270d3cae45/
http://autobuild.buildroot.net/results/a96/a969fd15a652df96c2414cf0c5f2e345d38e6e6c/
http://autobuild.buildroot.net/results/9ba/9ba92c01b2c6b6eae2dcda60c2b80d66d2002d4b/
http://autobuild.buildroot.net/results/776/776394ba89070ee2fa6e81585078df0a0e2ae3f2/

And many more.

SDL_mixer uses symbols from SDL, but ends up after it on the link cmdline,
breaking static linking. Fix it by forcing the SDL libs at the very end.

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/prboom/prboom.mk

@@ -15,6 +15,12 @@ ifeq ($(BR2_PACKAGE_LIBPNG),y)
 PRBOOM_DEPENDENCIES += libpng
 endif
 
+ifeq ($(BR2_STATIC_LIBS),y)
+# SDL_mixer uses symbols from SDL, but ends up after it on the link
+# cmdline. Fix it by forcing the SDL libs at the very end
+PRBOOM_CONF_ENV += LIBS="$(shell $(STAGING_DIR)/usr/bin/sdl-config --static-libs)"
+endif
+
 PRBOOM_CONF_OPTS = \
 		--oldincludedir=$(STAGING_DIR)/usr/include \
 		--with-sdl-prefix=$(STAGING_DIR)/usr \