Bazel build error

[didierbergeron]

Hello all,
Trying to do the bazel build as explained here and I get this error. Any idea what to do?
Is it because of my XCode version?
Thanks

ERROR: /private/var/tmp/_bazel_dB/675819f2ab031bab33e5a2099e633071/external/local_config_cc/BUILD:50:5: in apple_cc_toolchain rule @local_config_cc//:cc-compiler-darwin_x86_64: Xcode version must be specified to use an Apple CROSSTOOL. If your Xcode version has changed recently, try: "bazel clean --expunge" to re-run Xcode configuration
ERROR: Analysis of target '//magenta/tools/pip:build_pip_package' failed; build aborted: Analysis of target '@local_config_cc//:cc-compiler-darwin_x86_64' failed; build aborted