Protect _pointerBitWidth conditionals from misparsing on older Swifts

Author: lorentey

Sources/Atomics/Primitives/Primitives.native.swift.gyb

@@ -39,7 +39,7 @@ internal func _atomicMemoryFence(
 % for (swiftType, builtinType, alignment) in nativePrimitives:
 
 %   if builtinType == "Int128":
-#if _pointerBitWidth(_64)
+#if compiler(>=5.9) && _pointerBitWidth(_64)
 %   end
 @usableFromInline
 @frozen
@@ -267,10 +267,10 @@ extension UnsafeMutablePointer where Pointee == ${swiftType} {
 % end
 % end
 
-#if _pointerBitWidth(_64)
+#if compiler(>=5.9) && _pointerBitWidth(_64)
 @usableFromInline internal typealias _AtomicIntStorage = _AtomicInt64Storage
 @usableFromInline internal typealias _AtomicDoubleWordStorage = _AtomicInt128Storage
-#elseif _pointerBitWidth(_32)
+#elseif compiler(>=5.9) && _pointerBitWidth(_32)
 @usableFromInline internal typealias _AtomicIntStorage = _AtomicInt32Storage
 @usableFromInline internal typealias _AtomicDoubleWordStorage = _AtomicInt64Storage
 #else

Sources/Atomics/Primitives/autogenerated/Primitives.native.swift

@@ -2110,7 +2110,7 @@ extension UnsafeMutablePointer where Pointee == _AtomicInt64Storage {
   }
 }
 
-#if _pointerBitWidth(_64)
+#if compiler(>=5.9) && _pointerBitWidth(_64)
 @usableFromInline
 @frozen
 @_alignment(16)
@@ -2438,10 +2438,10 @@ extension UnsafeMutablePointer where Pointee == _AtomicInt128Storage {
 }
 #endif
 
-#if _pointerBitWidth(_64)
+#if compiler(>=5.9) && _pointerBitWidth(_64)
 @usableFromInline internal typealias _AtomicIntStorage = _AtomicInt64Storage
 @usableFromInline internal typealias _AtomicDoubleWordStorage = _AtomicInt128Storage
-#elseif _pointerBitWidth(_32)
+#elseif compiler(>=5.9) && _pointerBitWidth(_32)
 @usableFromInline internal typealias _AtomicIntStorage = _AtomicInt32Storage
 @usableFromInline internal typealias _AtomicDoubleWordStorage = _AtomicInt64Storage
 #else

Sources/Atomics/Types/DoubleWord.swift

@@ -13,7 +13,7 @@
 #if ATOMICS_NATIVE_BUILTINS
 import Builtin
 
-#if _pointerBitWidth(_32)
+#if compiler(>=5.9) && _pointerBitWidth(_32)
 @frozen
 @_alignment(8)
 public struct DoubleWord {
@@ -29,7 +29,7 @@ public struct DoubleWord {
     self.second = second
   }
 }
-#elseif _pointerBitWidth(_64)
+#elseif compiler(>=5.9) && _pointerBitWidth(_64)
 @frozen
 @_alignment(16)
 public struct DoubleWord {