[libc++][NFC] Move concepts to a subheader.

D103357 added some new concepts. Since the header `<concepts>` has moved
all its concepts to a separate header these new concepts feel out of
place. Move them to the appropriate header.

Reviewed By: #libc, Quuxplusone, ldionne

Differential Revision: https://reviews.llvm.org/D109075

libcxx/include/__concepts/arithmetic.h

@@ -34,6 +34,15 @@ concept unsigned_integral = integral<_Tp> && !signed_integral<_Tp>;
 template<class _Tp>
 concept floating_point = is_floating_point_v<_Tp>;
 
+// Concept helpers for the internal type traits for the fundamental types.
+
+template <class _Tp>
+concept __libcpp_unsigned_integer = __libcpp_is_unsigned_integer<_Tp>::value;
+template <class _Tp>
+concept __libcpp_signed_integer = __libcpp_is_signed_integer<_Tp>::value;
+template <class _Tp>
+concept __libcpp_floating_point = __libcpp_is_floating_point<_Tp>::value;
+
 #endif // _LIBCPP_STD_VER > 17 && !defined(_LIBCPP_HAS_NO_CONCEPTS)
 
 _LIBCPP_END_NAMESPACE_STD

libcxx/include/__format/format_arg.h

@@ -10,12 +10,12 @@
 #ifndef _LIBCPP___FORMAT_FORMAT_ARG_H
 #define _LIBCPP___FORMAT_FORMAT_ARG_H
 
+#include <__concepts/arithmetic.h>
 #include <__config>
 #include <__format/format_error.h>
 #include <__format/format_fwd.h>
 #include <__functional_base>
 #include <__variant/monostate.h>
-#include <concepts>
 #include <string>
 #include <string_view>
 

libcxx/include/concepts

@@ -152,28 +152,10 @@ namespace std {
 #include <__concepts/swappable.h>
 #include <__concepts/totally_ordered.h>
 #include <__config>
-#include <type_traits>
 #include <version>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #pragma GCC system_header
 #endif
 
-_LIBCPP_BEGIN_NAMESPACE_STD
-
-#if _LIBCPP_STD_VER > 17 && !defined(_LIBCPP_HAS_NO_CONCEPTS)
-
-// Concept helpers for the internal type traits for the fundamental types.
-
-template <class _Tp>
-concept __libcpp_unsigned_integer = __libcpp_is_unsigned_integer<_Tp>::value;
-template <class _Tp>
-concept __libcpp_signed_integer = __libcpp_is_signed_integer<_Tp>::value;
-template <class _Tp>
-concept __libcpp_floating_point = __libcpp_is_floating_point<_Tp>::value;
-
-#endif // _LIBCPP_STD_VER > 17 && !defined(_LIBCPP_HAS_NO_CONCEPTS)
-
-_LIBCPP_END_NAMESPACE_STD
-
 #endif // _LIBCPP_CONCEPTS

libcxx/include/type_traits

@@ -789,9 +789,6 @@ _LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_integral_v
 
 #endif // __has_keyword(__is_integral)
 
-// __libcpp_is_signed_integer, __libcpp_is_unsigned_integer
-// <concepts> implements __libcpp_signed_integer, __libcpp_unsigned_integer
-
 // [basic.fundamental] defines five standard signed integer types;
 // __int128_t is an extended signed integer type.
 // The signed and unsigned integer types, plus bool and the