Fix conflicting actions error when specifying --host_macos_minimum_os

The flag was introduced in #13001 but not usable internally, because
the host flag was not saved when doing a transition.  Host flags
should be saved, like in:

https://github.com/bazelbuild/bazel/blob/master/src/main/java/com/google/devtools/build/lib/rules/cpp/CppOptions.java#L1212

PiperOrigin-RevId: 435091962
diff --git a/src/main/java/com/google/devtools/build/lib/rules/apple/AppleCommandLineOptions.java b/src/main/java/com/google/devtools/build/lib/rules/apple/AppleCommandLineOptions.java
index 3dedbc6..20be2cc 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/apple/AppleCommandLineOptions.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/apple/AppleCommandLineOptions.java
@@ -521,6 +521,9 @@
     host.applePlatforms = applePlatforms;
     host.incompatibleUseToolchainResolution = incompatibleUseToolchainResolution;
 
+    // Save host option for further use.
+    host.hostMacosMinimumOs = hostMacosMinimumOs;
+
     return host;
   }