[libc++][C++03] cherry-pick #104773 (#158244)

Author: philnik777

libcxx/include/__cxx03/__math/traits.h

@@ -121,16 +121,19 @@ _LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI bool isnan(long double __x) _NOEX
 
 // isnormal
 
-template <class _A1, __enable_if_t<is_floating_point<_A1>::value, int> = 0>
-_LIBCPP_NODISCARD _LIBCPP_HIDE_FROM_ABI bool isnormal(_A1 __x) _NOEXCEPT {
-  return __builtin_isnormal(__x);
-}
-
 template <class _A1, __enable_if_t<is_integral<_A1>::value, int> = 0>
 _LIBCPP_NODISCARD _LIBCPP_HIDE_FROM_ABI bool isnormal(_A1 __x) _NOEXCEPT {
   return __x != 0;
 }
 
+_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI bool isnormal(float __x) _NOEXCEPT { return __builtin_isnormal(__x); }
+
+_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI bool isnormal(double __x) _NOEXCEPT { return __builtin_isnormal(__x); }
+
+_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI bool isnormal(long double __x) _NOEXCEPT {
+  return __builtin_isnormal(__x);
+}
+
 // isgreater
 
 template <class _A1, class _A2, __enable_if_t<is_arithmetic<_A1>::value && is_arithmetic<_A2>::value, int> = 0>

libcxx/test/std/numerics/c.math/isnormal.pass.cpp

@@ -11,8 +11,6 @@
 // We don't control the implementation on windows
 // UNSUPPORTED: windows
 
-// XFAIL: FROZEN-CXX03-HEADERS-FIXME
-
 #include <cassert>
 #include <cmath>
 #include <limits>