Prefer libcxx overload

By using `_LIBCPP_PREFERRED_OVERLOAD` we make
sure that a given overload is a better match
than an otherwise equally good function
declaration.

Why is there an equally good function
declaration in the first place? Underlying the
Windows SDK is the UCRT, the universal C runtime,
which clang-cl makes use of. The UCRT should
provide only C library headers, but does on top
comes with overloads for all cv-unqualified floating
point types (float, double, long double) for
`std::signbit()` in https://github.com/microsoft/win32metadata/blob/e012b29924c53aa941fc010850b68331b0c3ea80/generation/WinSDK/RecompiledIdlHeaders/ucrt/corecrt_math.h#L309-L322.
In a certain way, this can be seen as a deviation
from the C standard. We need to work around it.

Author: robincaloudis

libcxx/include/__math/traits.h

@@ -38,7 +38,12 @@ _LIBCPP_NODISCARD inline _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI boo
 #endif
 }
 
-_LIBCPP_NODISCARD inline _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI bool signbit(float __x) _NOEXCEPT {
+_LIBCPP_NODISCARD inline _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI
+#ifdef _LIBCPP_PREFERRED_OVERLOAD
+_LIBCPP_PREFERRED_OVERLOAD
+#endif
+    bool
+    signbit(float __x) _NOEXCEPT {
 // TODO(LLVM 22): Remove `__builtin_copysign`-workaround once support for Clang 19 is dropped.
 #if !__has_constexpr_builtin(__builtin_signbit) && _LIBCPP_STD_VER >= 23
   return __builtin_copysign(1.0, __x) == -1.0;
@@ -47,7 +52,12 @@ _LIBCPP_NODISCARD inline _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI boo
 #endif
 }
 
-_LIBCPP_NODISCARD inline _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI bool signbit(double __x) _NOEXCEPT {
+_LIBCPP_NODISCARD inline _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI
+#ifdef _LIBCPP_PREFERRED_OVERLOAD
+_LIBCPP_PREFERRED_OVERLOAD
+#endif
+    bool
+    signbit(double __x) _NOEXCEPT {
 // TODO(LLVM 22): Remove `__builtin_copysign`-workaround once support for Clang 19 is dropped.
 #if !__has_constexpr_builtin(__builtin_signbit) && _LIBCPP_STD_VER >= 23
   return __builtin_copysign(1.0, __x) == -1.0;
@@ -56,7 +66,12 @@ _LIBCPP_NODISCARD inline _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI boo
 #endif
 }
 
-_LIBCPP_NODISCARD inline _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI bool signbit(long double __x) _NOEXCEPT {
+_LIBCPP_NODISCARD inline _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI
+#ifdef _LIBCPP_PREFERRED_OVERLOAD
+_LIBCPP_PREFERRED_OVERLOAD
+#endif
+    bool
+    signbit(long double __x) _NOEXCEPT {
 // TODO(LLVM 22): Remove `__builtin_copysign`-workaround once support for Clang 19 is dropped.
 #if !__has_constexpr_builtin(__builtin_signbit) && _LIBCPP_STD_VER >= 23
   return __builtin_copysign(1.0, __x) == -1.0;