Revert rust-lang#110 to fix iOS cross-compilation after rust-lang#158. Fixes rust-lang#173

In rust-lang#158, better support for using CMake's cross-compilation facilities was
added. This made the workaround added in rust-lang#110 for iOS not only unnecessary,
but actively harmful, in that it runs afoul of SDK validation checks in the
CMake iOS codepath.

Author: luser

src/lib.rs

@@ -660,12 +660,6 @@ impl Config {
                     panic!("unsupported msvc target: {}", target);
                 }
             }
-        } else if target.contains("apple-ios") || target.contains("apple-tvos") {
-            // These two flags prevent CMake from adding an OSX sysroot, which messes up compilation.
-            if !self.defined("CMAKE_OSX_SYSROOT") && !self.defined("CMAKE_OSX_DEPLOYMENT_TARGET") {
-                cmd.arg("-DCMAKE_OSX_SYSROOT=/");
-                cmd.arg("-DCMAKE_OSX_DEPLOYMENT_TARGET=");
-            }
         } else if target.contains("darwin") {
             if !self.defined("CMAKE_OSX_ARCHITECTURES") {
                 if target.contains("x86_64") {