This is based on the suggestion here:

  <https://sourceware.org/ml/libc-alpha/2015-11/msg00174.html>

diff -up glibc-2.22-517-g2eecc8a/math/test-signgam-finite-c99.c.armhfp glibc-2.22-517-g2eecc8a/math/test-signgam-finite-c99.c
--- glibc-2.22-517-g2eecc8a/math/test-signgam-finite-c99.c.armhfp	2015-11-09 17:30:15.873258439 +0100
+++ glibc-2.22-517-g2eecc8a/math/test-signgam-finite-c99.c	2015-11-09 17:31:04.806517973 +0100
@@ -18,6 +18,7 @@
 
 #undef _LIBC
 #undef _GNU_SOURCE
+#undef _Mlong_double_
 #define _ISOMAC
 
 #include <math.h>