Stop using APPLE_SDK_VERSION_OVERRIDE

Bazel is still setting it, but it's been deprecated for quite some time.
Other tools like Buildbarn also no longer use it to resolve copies of
Xcode during the build.

bazelbuild/bazel@0af1cba
buildbarn/bb-remote-execution@97cfb22

The existing logic is a bit problematic when trying to use these rules
in combination with SDKs that don't follow the '${name}${version}'
structure.

Author: EdSchouten

foreign_cc/private/framework.bzl

@@ -340,15 +340,12 @@ def get_env_prelude(ctx, installdir, data_dependencies, tools_env):
 
     # This logic mirrors XcodeLocalEnvProvider#querySdkRoot in bazel itself
     if "APPLE_SDK_PLATFORM" in cc_env:
-        platform = cc_env["APPLE_SDK_PLATFORM"]
-        version = cc_env["APPLE_SDK_VERSION_OVERRIDE"]
-        sdk = "{}{}".format(platform.lower(), version)
         env_snippet.extend([
             # TODO: This path needs to take cc_env["XCODE_VERSION_OVERRIDE"] into account
             # Declare and export separately so bash doesn't ignore failures from the commands https://github.com/koalaman/shellcheck/wiki/SC2155
             "developer_dir_tmp=\"$(xcode-select --print-path)\"",
             "export DEVELOPER_DIR=\"$developer_dir_tmp\"",
-            "sdkroot_tmp=\"$(xcrun --sdk {} --show-sdk-path)\"".format(sdk),
+            "sdkroot_tmp=\"$(xcrun --sdk {} --show-sdk-path)\"".format(cc_env["APPLE_SDK_PLATFORM"].lower()),
             "export SDKROOT=\"$sdkroot_tmp\"",
             "export CMAKE_OSX_ARCHITECTURES={}".format(ctx.fragments.apple.single_arch_cpu),
         ])