This recent change seems to have broken builds that end up including /usr/include/bits/mathinline.h:

@@ -35,14 +35,16 @@
 __MATH_INLINE int
 __NTH (__signbitf (float __x))
 {
-  __extension__ union { float __f; int __i; } __u = { __f: __x };
-  return __u.__i < 0;
+  int __m;
+  asm ("pmovmskb %1, %0" : "=r" (__m) : "x" (__x));
+  return __m & 0x8;
 }

See end of these logs:

http://koji.fedoraproject.org/koji/getfile?taskID=1642229&name=build.log

glibc-2.10.90-17.x86_64 is broken

glibc-2.10.90-15.x86_64 works fine