From 7887dc0c7690b277d4c138d5e27d925cff26c4cd Mon Sep 17 00:00:00 2001
From: Joshua Haberman <jhaberman@gmail.com>
Date: Mon, 17 May 2021 15:56:38 -0700
Subject: [PATCH] Fixed the __has_attribute() check for old versions of Clang.

---
 upb/port_def.inc | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/upb/port_def.inc b/upb/port_def.inc
index 0f9a157bea..75d416d1ce 100644
--- a/upb/port_def.inc
+++ b/upb/port_def.inc
@@ -167,12 +167,20 @@
 
 /* Configure whether fasttable is switched on or not. *************************/
 
-#if defined(__clang__) && __has_attribute(musttail)
+#ifdef __has_attribute
+#define UPB_HAS_ATTRIBUTE(x) __has_attribute(x)
+#else
+#define UPB_HAS_ATTRIBUTE(x) 0
+#endif
+
+#if UPB_HAS_ATTRIBUTE(musttail)
 #define UPB_MUSTTAIL __attribute__((musttail))
 #else
 #define UPB_MUSTTAIL
 #endif
 
+#undef UPB_HAS_ATTRIBUTE
+
 /* This check is not fully robust: it does not require that we have "musttail"
  * support available. We need tail calls to avoid consuming arbitrary amounts
  * of stack space.