Fix the mac build for leopard users of the npapi/xpcom plugins.

Review at http://gwt-code-reviews.appspot.com/1323802


git-svn-id: https://google-web-toolkit.googlecode.com/svn/trunk@9641 8db76d5a-ed1c-0410-87a9-c151d255dfc7
diff --git a/plugins/xpcom/Makefile b/plugins/xpcom/Makefile
index 6ffcf7a..7a07984 100644
--- a/plugins/xpcom/Makefile
+++ b/plugins/xpcom/Makefile
@@ -24,7 +24,7 @@
 DEFAULT_FIREFOX_LIBS ?= /Applications/Firefox.app/Contents/MacOS
 RUN_PATH_FLAG = -executable_path
 DLL_SUFFIX = .dylib
-DLLFLAGS += -bundle $(ALLARCHCFLAGS)
+DLLFLAGS += -bundle $(ALLARCHCFLAGS) -mmacosx-version-min=10.5
 CFLAGS += $(ALLARCHCFLAGS)
 CXXFLAGS += $(ALLARCHCFLAGS)
 TARGET_PLATFORM = Darwin-gcc3