ext2fuse has been broken for a while because it's an old piece
of code that needs a few cflags for clang. Macports also defines
a different precompiler variable, `-D__FreeBSD__=10` which it
turns out fixes all our build errors and aslo fixes the need we
had for defining `SSIZE_T`
- Add to CFLAGS `-D__FreeBSD__=10 -DENABLE_SWAPFS` like MP.
- Add a `--std=gnu89` flag if compiler is clang
- Remove the unneeded CFLAG.
- Works great with superenv.
FixesHomebrew/homebrew#12207ClosesHomebrew/homebrew#15070.
Signed-off-by: Adam Vandenberg <flangy@gmail.com>
