Removed no longer needed flags when building on Windows

Ignore-this: 1d2b6f4332376160972ae3d31084ec37

darcs-hash:20140724094644-56b4d-de34688cddaebf7b632bb80d4b463f594877ba47
Fix compilation on OSX 10.9

Ignore-this: 8b0805336e1984203e396d3fd715adfb

- Set the isysroot also on LDFLAGS so that the linker looks in /path to SDK/usr/lib
- Simplify code by not duplicating flags, they are the in the beginning so they'll also
  be available when the environment is copied later

darcs-hash:20140724121107-56b4d-799fa116be611dd188c55db8c5b099d6b5354db8
Updated documentation for building on Windows

Ignore-this: a7f4f1dad0c3cf45d6037a5e84e0993f

darcs-hash:20140724141037-56b4d-9508ef74b2007563ef6dddad59697a16e9e5e23d