Enable searching for assemblies in GAC_Arm64 on Windows (PowerShell#17816)

Author: SteveL-MSFT

src/System.Management.Automation/CoreCLR/CorePsAssemblyLoadContext.cs

@@ -365,14 +365,14 @@ private bool TryFindInGAC(AssemblyName assemblyName, out string assemblyFilePath
 
             if (!assemblyFound)
             {
-                string gacBitnessAwarePath = null;
+                string gacBitnessAwarePath;
 
                 if (Environment.Is64BitProcess)
                 {
                     if (string.IsNullOrEmpty(_gacPath64))
                     {
-                        // cache value of '_gacPath64' folder in member variable.
-                        _gacPath64 = $"{_winDir}{dirSeparator}Microsoft.NET{dirSeparator}assembly{dirSeparator}GAC_64";
+                       var gacName = RuntimeInformation.ProcessArchitecture == Architecture.Arm64 ? "GAC_Arm64" : "GAC_64";
+                        _gacPath64 = Path.Join(_winDir, "Microsoft.NET", "assembly", gacName);
                     }
 
                     gacBitnessAwarePath = _gacPath64;
@@ -381,8 +381,7 @@ private bool TryFindInGAC(AssemblyName assemblyName, out string assemblyFilePath
                 {
                     if (string.IsNullOrEmpty(_gacPath32))
                     {
-                        // cache value of '_gacPath32' folder in member variable.
-                        _gacPath32 = $"{_winDir}{dirSeparator}Microsoft.NET{dirSeparator}assembly{dirSeparator}GAC_32";
+                        _gacPath32 = Path.Join(_winDir, "Microsoft.NET", "assembly", "GAC_32");
                     }
 
                     gacBitnessAwarePath = _gacPath32;