[SystemZ] Disable float16-smoke.c test

Clang on s390x now supports _Float16, and therefore the test is now
attempted.  However the system libraries on current distributions
do not yet contain the necessary conversion routines to actually run
binaries using _Float16, and so the attempt fails.

Disable the test on s390x for now.

Author: uweigand

SingleSource/Regression/C/float16-smoke.c

@@ -1,7 +1,11 @@
 #include <stdio.h>
 
 
-#ifdef __FLT16_DIG__
+// Clang on s390x now supports _Float16, however the system libraries
+// on current distributions do not yet contain the necessary conversion
+// routines to actually run binaries using _Float16.  Disable the test
+// on s390x for now.
+#if defined(__FLT16_DIG__) && !defined(__s390x__)
 
 typedef _Float16 fp16_t;
 __attribute__((noinline))