Redmine #5211: Detect broken strndup on AIX and provide workaround.

But how do you know what else is allocated in the page? Glibc might allocate all sorts of things behind your back. All it takes for memcmp to crash is for it to happen to be crossing a page boundary (depending a bit on malloc's brk() strategy, but still). And we have to look out for *all* platforms in this case. My test is guaranteed to work on any conforming platform, and has been verified to crash on AIX. So I think my test is more reliable.

I could of course raise it ridiculously high, like 2GB, to be *absolutely sure*! I doubt even a 64-bit system will allocate that much virtual space "just in case". :-)