Trust xcrun now that we error out early for bad xcode-select paths

Since ae177adb2bd55ee5ad6367e7639c4cf0c774b63a, we can safely assume
that xcrun works, and a functioning xcrun will search dev_tools_path and
xctoolchain_path, so we can stop doing extra work here.

On CLT-only 10.7 and 10.8, xcrun will not work, but all the tools will
be in /usr/bin, which we check before invoking xcrun. Further, in this
case, dev_tools_path will be /usr/bin, and xctoolchain_path will not
exist, so the fallbacks here are unnecessary.

Library/Homebrew/os/mac.rb

@@ -27,25 +27,11 @@ module OS
         @locate[key] = if File.executable?(path = "/usr/bin/#{tool}")
           Pathname.new path
         # Homebrew GCCs most frequently; much faster to check this before xcrun
-        # This also needs to be queried if xcrun won't work, e.g. CLT-only
         elsif File.executable?(path = "#{HOMEBREW_PREFIX}/bin/#{tool}")
           Pathname.new path
         else
-          # If the tool isn't in /usr/bin or from Homebrew,
+          path = `/usr/bin/xcrun -no-cache -find #{tool} 2>/dev/null`.chomp
-          # then we first try to use xcrun to find it.
+          Pathname.new(path) if File.executable?(path)
-          # If it's not there, or xcode-select is misconfigured, we have to
-          # look in dev_tools_path, and finally in xctoolchain_path, because the
-          # tools were split over two locations beginning with Xcode 4.3+.
-          xcrun_path = begin
-            path = `/usr/bin/xcrun -find #{tool} 2>/dev/null`.chomp
-            # If xcrun finds a superenv tool then discard the result.
-            path unless path.include?("Library/ENV")
-          end
-
-          paths = %W[#{xcrun_path}
-                    #{dev_tools_path}/#{tool}
-                    #{xctoolchain_path}/usr/bin/#{tool}]
-          paths.map { |p| Pathname.new(p) }.find { |p| p.executable? }
         end
       end
     end