tgmath.h: disable builtins

Signed-off-by: Peter S. Mazinger <ps.m@gmx.net>
Signed-off-by: Bernhard Reutner-Fischer <rep.dot.nop@gmail.com>

include/tgmath.h

@@ -48,7 +48,7 @@
 
 /* 1 if 'type' is a floating type, 0 if 'type' is an integer type.
    Allows for _Bool.  Expands to an integer constant expression.  */
-# if __GNUC_PREREQ (3, 1)
+# if 0 /* __GNUC_PREREQ (3, 1) */
 #  define __floating_type(type) \
   (__builtin_classify_type ((type) 0) == 8 \
    || (__builtin_classify_type ((type) 0) == 9 \