stdlib: fix the #if guard for Builtin.unprotectedStackAlloc

rdar://107274878

Author: eeckstein

stdlib/public/core/TemporaryAllocation.swift

@@ -161,7 +161,6 @@ internal func _withUnsafeTemporaryAllocation<T, R>(
 #endif
 }
 
-#if $BuiltinUnprotectedStackAlloc
 @_alwaysEmitIntoClient @_transparent
 internal func _withUnprotectedUnsafeTemporaryAllocation<T, R>(
   of type: T.Type,
@@ -181,11 +180,19 @@ internal func _withUnprotectedUnsafeTemporaryAllocation<T, R>(
   // notice and complain.)
   let result: R
 
+#if $BuiltinUnprotectedStackAlloc
   let stackAddress = Builtin.unprotectedStackAlloc(
     capacity._builtinWordValue,
     MemoryLayout<T>.stride._builtinWordValue,
     alignment._builtinWordValue
   )
+#else
+  let stackAddress = Builtin.stackAlloc(
+    capacity._builtinWordValue,
+    MemoryLayout<T>.stride._builtinWordValue,
+    alignment._builtinWordValue
+  )
+#endif
 
   // The multiple calls to Builtin.stackDealloc() are because defer { } produces
   // a child function at the SIL layer and that conflicts with the verifier's
@@ -200,7 +207,6 @@ internal func _withUnprotectedUnsafeTemporaryAllocation<T, R>(
     throw error
   }
 }
-#endif
 
 @_alwaysEmitIntoClient @_transparent
 internal func _fallBackToHeapAllocation<R>(
@@ -281,20 +287,16 @@ public func _withUnprotectedUnsafeTemporaryAllocation<R>(
   alignment: Int,
   _ body: (UnsafeMutableRawBufferPointer) throws -> R
 ) rethrows -> R {
-  return try _withUnsafeTemporaryAllocation(
+  return try _withUnprotectedUnsafeTemporaryAllocation(
     of: Int8.self,
     capacity: byteCount,
     alignment: alignment
   ) { pointer in
-#if $BuiltinUnprotectedStackAlloc
     let buffer = UnsafeMutableRawBufferPointer(
       start: .init(pointer),
       count: byteCount
     )
     return try body(buffer)
-#else
-    return try withUnsafeTemporaryAllocation(byteCount: byteCount, alignment: alignment, body)
-#endif
   }
 }
 
@@ -365,15 +367,11 @@ public func _withUnprotectedUnsafeTemporaryAllocation<T, R>(
     capacity: capacity,
     alignment: MemoryLayout<T>.alignment
   ) { pointer in
-#if $BuiltinUnprotectedStackAlloc
     Builtin.bindMemory(pointer, capacity._builtinWordValue, type)
     let buffer = UnsafeMutableBufferPointer<T>(
       start: .init(pointer),
       count: capacity
     )
     return try body(buffer)
-#else
-    return try withUnsafeTemporaryAllocation(of: type, capacity: capacity, body)
-#endif
   }
 }