[windows][lldb] fix incorrect LLVM_HOST_TRIPLE when cross-compiling

Author: charles-zablit

utils/build.ps1

@@ -1834,7 +1834,7 @@ function Get-CompilersDefines([Hashtable] $Platform, [string] $Variant, [switch]
     LLVM_CONFIG_PATH = (Join-Path -Path $BuildTools -ChildPath "llvm-config.exe");
     LLVM_ENABLE_ASSERTIONS = $(if ($Variant -eq "Asserts") { "YES" } else { "NO" })
     LLVM_EXTERNAL_SWIFT_SOURCE_DIR = "$SourceCache\swift";
-    LLVM_HOST_TRIPLE = $BuildPlatform.Triple;
+    LLVM_HOST_TRIPLE = $Platform.Triple;
     LLVM_NATIVE_TOOL_DIR = $BuildTools;
     LLVM_TABLEGEN = (Join-Path $BuildTools -ChildPath "llvm-tblgen.exe");
     LLVM_USE_HOST_TOOLS = "NO";