fix hypot tests

[Bruno Haible]

On FreeBSD 11.0/x86 I'm seeing these test failures:

FAIL: test-hypot
================

../../gltests/test-hypot.h:41: assertion 'z == HUGEVAL' failed
FAIL test-hypot (exit status: 134)

FAIL: test-hypotf
=================

../../gltests/test-hypot.h:41: assertion 'z == HUGEVAL' failed
FAIL test-hypotf (exit status: 134)


This patch fixes it:


2017-08-17  Bruno Haible  <br...@clisp.org>

        hypot tests: Fix test failure on FreeBSD 11.0/x86.
        * tests/test-hypot.h (test_function): Declare z as 'volatile'.

diff --git a/tests/test-hypot.h b/tests/test-hypot.h
index cfd0aec..1ee790f 100644
--- a/tests/test-hypot.h
+++ b/tests/test-hypot.h
@@ -32,7 +32,7 @@ test_function (void)
   {
     volatile DOUBLE x;
     volatile DOUBLE y;
-    DOUBLE z;
+    volatile DOUBLE z;
 
     /* Overflow.  */
     x = MAX;