AFAICS from the CVS history, -fno-common has been there on OSX only since the 2000, when the build was made to work on OSX. I see no reason to keep it, especially considering we don't use the flag on other platforms. It also breaks my jemalloc3 queue because I rely on -fcommon to override jemalloc overridable variables (thus avoiding modifying jemalloc upstream source code and possible future merge conflicts). I could remove -fno-common when building jemalloc only, but I don't think it hurts to just remove it completely.
Created attachment 620635 [details] [diff] [review] Don't use the -fno-common flag
Created attachment 620718 [details] [diff] [review] Don't use the -fno-common flag