PR6515: Implement __builtin_signbit and friends.

I'm reasonably sure my implementation is correct, but it would be nice if
someone could double-check.



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@97864 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/test/CodeGen/builtins.c b/test/CodeGen/builtins.c
index 417ca7d..a4424d7 100644
--- a/test/CodeGen/builtins.c
+++ b/test/CodeGen/builtins.c
@@ -118,6 +118,7 @@
   // V(clear_cache, (&N, &N+1));
   V(trap, ());
   R(extract_return_addr, (&N));
+  P(signbit, (1.0));
 
   return 0;
 }