Note that Command Line Tools for Xcode suffices

Godot does not require the full Xcode package to build, only the Command Line Tools for Xcode, so this modifies the build instructions to make that clear.

reference/compiling_for_osx.rst

@@ -13,7 +13,7 @@ required:
 
 -  Python 2.7+ (3.0 is untested as of now)
 -  SCons build system
--  XCode
+-  Xcode (or the more lightweight Command Line Tools for Xcode)
 
 Compiling
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