bpo-41617: Fix pycore_bitutils.h to support clang 3.0 (GH-22042)

__builtin_bswap16() is not available in LLVM clang 3.0.

Author: vstinner

Include/internal/pycore_bitutils.h

@@ -17,10 +17,12 @@ extern "C" {
 #  error "this header requires Py_BUILD_CORE define"
 #endif
 
-#if defined(__clang__) || \
-    (defined(__GNUC__) && \
-     ((__GNUC__ >= 5) || (__GNUC__ == 4) && (__GNUC_MINOR__ >= 8)))
-   /* __builtin_bswap16() is available since GCC 4.8,
+#if ((defined(__GNUC__) \
+      && ((__GNUC__ >= 5) || (__GNUC__ == 4) && (__GNUC_MINOR__ >= 8))) \
+     || (defined(__clang__) \
+         && (__clang_major__ >= 4 \
+             || (__clang_major__ == 3 && __clang_minor__ >= 2))))
+   /* __builtin_bswap16() is available since GCC 4.8 and clang 3.2,
       __builtin_bswap32() is available since GCC 4.3,
       __builtin_bswap64() is available since GCC 4.3. */
 #  define _PY_HAVE_BUILTIN_BSWAP

Misc/NEWS.d/next/Build/2020-08-24-18-34-01.bpo-41617.sKKXz7.rst

@@ -0,0 +1,2 @@
+Fix ``pycore_bitutils.h`` header file to support old clang versions:
+``__builtin_bswap16()`` is not available in LLVM clang 3.0.