Correctly get the arguments and environment, even for processes that have a...

Correctly get the arguments and environment, even for processes that have a large amount or arguments and/or environment variables.

We previously passed in a 8192 byte buffer but this wasn't large enough. We now calculate the size we need and then add 128 to it and get the environment. If we pass exactly the number of bytes it says is needs, the sysctl() returns junk. Adding 1 seemed to do the trick, but to err on the side of caution, I added a few bytes more.

<rdar://problem/21883842>

llvm-svn: 242729