Fix conflicting actions error when specifying --host_macos_minimum_os (#15068)

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
(cherry picked from commit b8a2ee2ca8ae1f66b40baea8fc413b2732e7ebaa)

Co-authored-by: waltl <waltl@google.com>
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 ceef262..13bfeec 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
@@ -511,6 +511,9 @@
     host.includeXcodeExecutionRequirements = includeXcodeExecutionRequirements;
     host.appleCrosstoolTop = appleCrosstoolTop;
 
+    // Save host option for further use.
+    host.hostMacosMinimumOs = hostMacosMinimumOs;
+
     return host;
   }