[Support] Consolidate runOnNewStack (NFC) (llvm#160816)

This patch consolidates two implementations of runOnNewStack with "if constexpr".

Author: kazutakahirata

llvm/include/llvm/Support/ProgramStack.h

@@ -46,17 +46,15 @@ LLVM_ABI unsigned getDefaultStackSize();
 LLVM_ABI void runOnNewStack(unsigned StackSize, function_ref<void()> Fn);
 
 template <typename R, typename... Ts>
-std::enable_if_t<!std::is_same_v<R, void>, R>
-runOnNewStack(unsigned StackSize, function_ref<R(Ts...)> Fn, Ts &&...Args) {
- std::optional<R> Ret;
- runOnNewStack(StackSize, [&]() { Ret = Fn(std::forward<Ts>(Args)...); });
- return std::move(*Ret);
-}
-
-template <typename... Ts>
-void runOnNewStack(unsigned StackSize, function_ref<void(Ts...)> Fn,
+auto runOnNewStack(unsigned StackSize, function_ref<R(Ts...)> Fn,
  Ts &&...Args) {
- runOnNewStack(StackSize, [&]() { Fn(std::forward<Ts>(Args)...); });
+ if constexpr (std::is_same_v<R, void>) {
+ runOnNewStack(StackSize, [&]() { Fn(std::forward<Ts>(Args)...); });
+ } else {
+ std::optional<R> Ret;
+ runOnNewStack(StackSize, [&]() { Ret = Fn(std::forward<Ts>(Args)...); });
+ return std::move(*Ret);
+ }
 }
 
 } // namespace llvm