Prevent Arm64 CrossDac builds running on Arm64. (#88467)

* Prevent Arm64 CrossDac builds running on Arm64.

Currently, when building the CLR on win-arm64, CrossDac builds for
Linux with an (incorrect) host arch of x64 are attempted, failing
the build. This patch prevents those builds running on systems with
an identical host architecture to the cross target.

* Revert to simpler strategy of simply ignoring when arch != x86|x64.

eng/Subsets.props

@@ -277,7 +277,7 @@
     <CrossDacHostArch Condition="'$(TargetArchitecture)' == 'arm'">x86</CrossDacHostArch>
   </PropertyGroup>
 
-  <ItemGroup Condition="$(_subset.Contains('+linuxdac+')) and $([MSBuild]::IsOsPlatform(Windows)) and '$(TargetArchitecture)' != 'x86'">
+  <ItemGroup Condition="$(_subset.Contains('+linuxdac+')) and $([MSBuild]::IsOsPlatform(Windows))  and ('$(BuildArchitecture)' == 'x64' or '$(BuildArchitecture)' == 'x86') and '$(TargetArchitecture)' != 'x86'">
     <ProjectToBuild
       Include="$(CoreClrProjectRoot)runtime.proj"
       AdditionalProperties="%(AdditionalProperties);
@@ -289,7 +289,7 @@
                             CMakeArgs=$(CMakeArgs) -DCLR_CROSS_COMPONENTS_BUILD=1" Category="clr" />
   </ItemGroup>
 
-  <ItemGroup Condition="$(_subset.Contains('+alpinedac+')) and $([MSBuild]::IsOsPlatform(Windows)) and '$(TargetArchitecture)' != 'x86'">
+  <ItemGroup Condition="$(_subset.Contains('+alpinedac+')) and $([MSBuild]::IsOsPlatform(Windows)) and ('$(BuildArchitecture)' == 'x64' or '$(BuildArchitecture)' == 'x86') and '$(TargetArchitecture)' != 'x86'">
     <ProjectToBuild
       Include="$(CoreClrProjectRoot)runtime.proj"
       AdditionalProperties="%(AdditionalProperties);