[llvm] Create UEFI helper function

Create useful helper function for UEFI 64 bit target that can be used in
tablegen files in future changes.

Author: Prabhuk

llvm/lib/Target/X86/X86Subtarget.h

@@ -331,7 +331,9 @@ class X86Subtarget final : public X86GenSubtargetInfo {
 
   bool isOSWindows() const { return TargetTriple.isOSWindows(); }
 
-  bool isOSWindowsOrUEFI() const { return isOSWindows() || isUEFI(); }
+  bool isOSWindowsOrUEFI() const { return TargetTriple.isOSWindowsOrUEFI(); }
+
+  bool isTargetUEFI64() const { return Is64Bit && isUEFI(); }
 
   bool isTargetWin64() const { return Is64Bit && isOSWindows(); }