[xabt] Fix _TouchAndroidLinkFlag target skipping on NativeAOT incremental builds (#10849)

Add '$(RunILLink)' != 'false' to the Condition of _TouchAndroidLinkFlag
so it Condition-skips in lockstep with the ILLink target it hooks via
AfterTargets. This works around an MSBuild behavior (dotnet/msbuild#13274)
where AfterTargets hooks may fire before the target actually executes,
leading to a stale flag.

Without this fix, _TouchAndroidLinkFlag's Inputs/Outputs check sees
stale timestamps on the first (skipped) ILLink invocation and skips
itself, then never runs again when ILLink actually executes.  This
can sometimes cause link.flag to go stale, which can cause
_RemoveRegisterAttribute and the AssemblyModifierPipeline to skip on
incremental builds.

Author: sbomer

src/Xamarin.Android.Build.Tasks/Microsoft.Android.Sdk/targets/Microsoft.Android.Sdk.TypeMap.LlvmIr.targets

@@ -243,7 +243,7 @@
 
   <Target Name="_TouchAndroidLinkFlag"
       AfterTargets="ILLink"
-      Condition=" '$(PublishTrimmed)' == 'true' and Exists('$(_LinkSemaphore)') "
+      Condition=" '$(PublishTrimmed)' == 'true' and '$(RunILLink)' != 'false' and Exists('$(_LinkSemaphore)') "
       Inputs="$(_LinkSemaphore)"
       Outputs="$(_AndroidLinkFlag)">
     <!-- This file is an input for _RemoveRegisterAttribute -->