[llvm] Allow Fast and Tail CC in UEFI

Allow tail call and fastcc optimizations for UEFI X86_64 targets.

Author: Prabhuk

llvm/lib/Target/X86/X86Subtarget.h

@@ -352,9 +352,9 @@ class X86Subtarget final : public X86GenSubtargetInfo {
     switch (CC) {
     // On Win64, all these conventions just use the default convention.
     case CallingConv::C:
-      return isTargetWin64() || isTargetUEFI64();
     case CallingConv::Fast:
     case CallingConv::Tail:
+      return isTargetWin64() || isTargetUEFI64();
     case CallingConv::Swift:
     case CallingConv::SwiftTail:
     case CallingConv::X86_FastCall: