Revert "x86: Do not use __builtin_isinf_sign for _Float64x/long double"

This reverts commit 999cd617cb.  It
breaks libstdc++ and other languages bootstrap.

Reviewed-by: Carlos O'Donell <carlos@redhat.com>

bits/fp-builtin-denormal.h

@@ -26,7 +26,3 @@
     Intel double extended-precision (long double).  By default assume 1 to
     enable the usage of compiler builtin on math.h.  */
 #define __FP_BUILTIN_FPCLASSIFY_DENORMAL 1
-
-/* __FP_BUILTIN_ISINF_SIGN_DENORMAL is defined to 1 if compiler supports
-   handling pseudo-dernormal numbers with isinf_sign builtin.  */
-#define __FP_BUILTIN_ISINF_SIGN_DENORMAL 1

math/math.h

@@ -1249,10 +1249,7 @@ enum
      ? __isinff128 (x) : __builtin_isinf_sign (x))
 # elif (__GNUC_PREREQ (4,4) && !defined __SUPPORT_SNAN__) \
        || __glibc_clang_prereq (3,7)
-#  define isinf(x) __MATH_TG_BUILTIN_CLASSIFY ((x),			      \
-					       __builtin_isinf_sign, (x),     \
-					       isinf, (x),		      \
-					       __FP_BUILTIN_ISINF_SIGN_DENORMAL)
+#  define isinf(x) __builtin_isinf_sign (x)
 # else
 #  define isinf(x) __MATH_TG ((x), __isinf, (x))
 # endif

sysdeps/x86/bits/fp-builtin-denormal.h

@@ -23,7 +23,3 @@
 /* Neither GCC (bug 123161) nor clang (issue 172533) handles pseudo-normal
    numbers correctly with fpclassify builtin.  */
 #define __FP_BUILTIN_FPCLASSIFY_DENORMAL 0
-
-/* Neither GCC (bug 123173) nor clang (issue 172651) handles pseudo-normal
-   numbers correctly with isinf_sign builtin.  */
-#define __FP_BUILTIN_ISINF_SIGN_DENORMAL 0

sysdeps/x86/fpu/test-builtin-denormal.c

@@ -45,10 +45,6 @@ do_test (void)
       TEST_COMPARE (feclearexcept (FE_INVALID), 0);
       TEST_COMPARE (fpclassify (inputs[i].value), FP_NAN);
       TEST_COMPARE (fetestexcept (FE_INVALID), 0);
-
-      TEST_COMPARE (feclearexcept (FE_INVALID), 0);
-      TEST_COMPARE (isinf (inputs[i].value), 0);
-      TEST_COMPARE (fetestexcept (FE_INVALID), 0);
     }
 
   return 0;