Make Bazel's osx crosstool more resilient against missing variables
Make Bazel's osx crosstool more resilient against missing variables

RELNOTES: None.
PiperOrigin-RevId: 209556782

dslomov/bazel-windows,ulfjack/bazel,cushon/bazel,cushon/bazel,aehlig/bazel,dslomov/bazel-windows,katre/bazel,twitter-forks/bazel,safarmer/bazel,dslomov/bazel-windows,perezd/bazel,meteorcloudy/bazel,ButterflyNetwork/bazel,akira-baruah/bazel,perezd/bazel,meteorcloudy/bazel,dslomov/bazel,dslomov/bazel,katre/bazel,meteorcloudy/bazel,meteorcloudy/bazel,aehlig/bazel,katre/bazel,ButterflyNetwork/bazel,safarmer/bazel,davidzchen/bazel,bazelbuild/bazel,perezd/bazel,aehlig/bazel,bazelbuild/bazel,akira-baruah/bazel,katre/bazel,ButterflyNetwork/bazel,davidzchen/bazel,dslomov/bazel-windows,ButterflyNetwork/bazel,bazelbuild/bazel,werkt/bazel,safarmer/bazel,akira-baruah/bazel,perezd/bazel,aehlig/bazel,akira-baruah/bazel,werkt/bazel,davidzchen/bazel,werkt/bazel,twitter-forks/bazel,safarmer/bazel,werkt/bazel,davidzchen/bazel,cushon/bazel,perezd/bazel,bazelbuild/bazel,twitter-forks/bazel,ulfjack/bazel,ulfjack/bazel,bazelbuild/bazel,dslomov/bazel-windows,werkt/bazel,safarmer/bazel,davidzchen/bazel,safarmer/bazel,katre/bazel,ulfjack/bazel,bazelbuild/bazel,aehlig/bazel,cushon/bazel,twitter-forks/bazel,dslomov/bazel,dslomov/bazel-windows,twitter-forks/bazel,dslomov/bazel,dslomov/bazel,ulfjack/bazel,twitter-forks/bazel,akira-baruah/bazel,dslomov/bazel,ulfjack/bazel,aehlig/bazel,meteorcloudy/bazel,aehlig/bazel,ulfjack/bazel,perezd/bazel,akira-baruah/bazel,dslomov/bazel,perezd/bazel,ButterflyNetwork/bazel,ButterflyNetwork/bazel,meteorcloudy/bazel,werkt/bazel,katre/bazel,davidzchen/bazel,twitter-forks/bazel,cushon/bazel,cushon/bazel,meteorcloudy/bazel,davidzchen/bazel