From 1f46b006b70bdbab899526f61bad238b5c651e36 Mon Sep 17 00:00:00 2001
From: Cory Fields <cory-nospam-@coryfields.com>
Date: Mon, 8 Dec 2014 19:08:49 -0500
Subject: [PATCH] build: fix __builtin_expect detection for clang

Using AC_CHECK_DECL, the generated test tries to cast the function to void.
Clang doesn't allow that for builtins.
---
 configure.ac | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/configure.ac b/configure.ac
index 60a5405..0083a91 100644
--- a/configure.ac
+++ b/configure.ac
@@ -103,7 +103,11 @@ AC_ARG_WITH([scalar], [AS_HELP_STRING([--with-scalar=64bit|32bit|auto],
 
 AC_CHECK_TYPES([__int128])
 
-AC_CHECK_DECL(__builtin_expect,AC_DEFINE(HAVE_BUILTIN_EXPECT,1,[Define this symbol if __builtin_expect is available]),,)
+AC_MSG_CHECKING([for __builtin_expect])
+AC_COMPILE_IFELSE([AC_LANG_SOURCE([[void myfunc() {__builtin_expect(0,0);}]])],
+    [ AC_MSG_RESULT([yes]);AC_DEFINE(HAVE_BUILTIN_EXPECT,1,[Define this symbol if __builtin_expect is available]) ],
+    [ AC_MSG_RESULT([no])
+    ])
 
 if test x"$req_field" = x"auto"; then
   SECP_64BIT_ASM_CHECK