Enable build on hosted arm64 (dotnet#40311)

Initialize HostArch to the arch-style used in RIDs directly. Unless
running in Visual Studio, when it should be forced to x64.

Initialize ArchGroup to HostArch unless overriden.

Use the HostArch for the tool runtime instead of assuming x64.

Author: omajid

Directory.Build.props

@@ -64,10 +64,10 @@
     <TargetGroup Condition="'$(TargetGroup)' == ''">netcoreapp</TargetGroup>
     <OSGroup Condition="'$(OSGroup)' == ''">$(DefaultOSGroup)</OSGroup>
     <ConfigurationGroup Condition="'$(ConfigurationGroup)' == ''">Debug</ConfigurationGroup>
-    <HostArch>$([System.Runtime.InteropServices.RuntimeInformation]::ProcessArchitecture)</HostArch>
-    <ArchGroup Condition="'$(ArchGroup)' == '' AND '$(HostArch)' == 'Arm'">arm</ArchGroup>
-    <ArchGroup Condition="'$(ArchGroup)' == '' AND '$(HostArch)' == 'Arm64'">arm64</ArchGroup>
-    <ArchGroup Condition="'$(ArchGroup)' == ''">x64</ArchGroup>
+    <HostArch>$([System.Runtime.InteropServices.RuntimeInformation]::ProcessArchitecture.ToString().ToLowerInvariant())</HostArch>
+    <!-- MSBuild inside Visual Studio is always x86. Force it to x64. -->
+    <HostArch Condition="'$(BuildingInsideVisualStudio)' == 'true'">x64</HostArch>
+    <ArchGroup Condition="'$(ArchGroup)' == ''">$(HostArch)</ArchGroup>
 
     <!-- Initialize BuildConfiguration from the individual properties if it wasn't already explicitly set -->
     <BuildConfiguration Condition="'$(BuildConfiguration)' == ''">$(TargetGroup)-$(OSGroup)-$(ConfigurationGroup)-$(ArchGroup)</BuildConfiguration>
@@ -135,9 +135,9 @@
     <_runtimeOS Condition="'$(_runtimeOS)' == 'tizen.4.0.0'">linux</_runtimeOS>
     <_runtimeOS Condition="'$(_runtimeOS)' == 'tizen.5.0.0'">linux</_runtimeOS>
     <_runtimeOS Condition="'$(PortableBuild)' == 'true'">$(_portableOS)</_runtimeOS>
-    <ToolRuntimeRID>$(_runtimeOS)-x64</ToolRuntimeRID>
+    <ToolRuntimeRID>$(_runtimeOS)-$(HostArch)</ToolRuntimeRID>
     <!-- We build linux-musl-arm on a ubuntu container, so we can't use the toolset build for alpine runtime. We need to use portable linux RID for our toolset in order to be able to use it. -->
-    <ToolRuntimeRID Condition="'$(_runtimeOS)' == 'linux-musl' AND $(ArchGroup.StartsWith('arm')) AND !$(HostArch.StartsWith('Arm'))">linux-x64</ToolRuntimeRID>
+    <ToolRuntimeRID Condition="'$(_runtimeOS)' == 'linux-musl' AND $(ArchGroup.StartsWith('arm')) AND !$(HostArch.StartsWith('arm'))">linux-x64</ToolRuntimeRID>
 
     <!-- There are no WebAssembly tools, so treat them as Windows -->
     <ToolRuntimeRID Condition="'$(RuntimeOS)' == 'WebAssembly'">win-x64</ToolRuntimeRID>