[libc++] Simplify <limits> a bit (#140021)

This does a few small things:
- inline `__libcpp_compute_min`, since we can don't have to put the
arithmetic behind a constraint. Simple arithmetic also tends to be
faster to compile than instantiating a type.
- Remove an unused include (and add missing includes elsewhere)
- Remove `__min` and `__max` from the `bool` specialization

Co-authored-by: Louis Dionne <ldionne.2@gmail.com>

Author: philnik777

libcxx/include/__numeric/gcd_lcm.h

@@ -10,7 +10,6 @@
 #ifndef _LIBCPP___NUMERIC_GCD_LCM_H
 #define _LIBCPP___NUMERIC_GCD_LCM_H
 
-#include <__algorithm/min.h>
 #include <__assert>
 #include <__bit/countr.h>
 #include <__config>
@@ -20,6 +19,7 @@
 #include <__type_traits/is_same.h>
 #include <__type_traits/is_signed.h>
 #include <__type_traits/make_unsigned.h>
+#include <__type_traits/remove_cv.h>
 #include <limits>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)

libcxx/include/forward_list

@@ -233,6 +233,7 @@ template <class T, class Allocator, class Predicate>
 #  include <__type_traits/is_pointer.h>
 #  include <__type_traits/is_same.h>
 #  include <__type_traits/is_swappable.h>
+#  include <__type_traits/remove_cv.h>
 #  include <__type_traits/type_identity.h>
 #  include <__utility/forward.h>
 #  include <__utility/move.h>

libcxx/include/limits

@@ -108,7 +108,6 @@ template<> class numeric_limits<cv long double>;
 #  include <__config>
 #  include <__type_traits/is_arithmetic.h>
 #  include <__type_traits/is_signed.h>
-#  include <__type_traits/remove_cv.h>
 
 #  if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #    pragma GCC system_header
@@ -178,16 +177,6 @@ protected:
   static _LIBCPP_CONSTEXPR const float_round_style round_style = round_toward_zero;
 };
 
-template <class _Tp, int __digits, bool _IsSigned>
-struct __libcpp_compute_min {
-  static _LIBCPP_CONSTEXPR const _Tp value = _Tp(_Tp(1) << __digits);
-};
-
-template <class _Tp, int __digits>
-struct __libcpp_compute_min<_Tp, __digits, false> {
-  static _LIBCPP_CONSTEXPR const _Tp value = _Tp(0);
-};
-
 template <class _Tp>
 class __libcpp_numeric_limits<_Tp, true> {
 protected:
@@ -199,7 +188,7 @@ protected:
   static _LIBCPP_CONSTEXPR const int digits       = static_cast<int>(sizeof(type) * __CHAR_BIT__ - is_signed);
   static _LIBCPP_CONSTEXPR const int digits10     = digits * 3 / 10;
   static _LIBCPP_CONSTEXPR const int max_digits10 = 0;
-  static _LIBCPP_CONSTEXPR const type __min       = __libcpp_compute_min<type, digits, is_signed>::value;
+  static _LIBCPP_CONSTEXPR const type __min       = is_signed ? _Tp(_Tp(1) << digits) : 0;
   static _LIBCPP_CONSTEXPR const type __max       = is_signed ? type(type(~0) ^ __min) : type(~0);
   [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI static _LIBCPP_CONSTEXPR type min() _NOEXCEPT { return __min; }
   [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI static _LIBCPP_CONSTEXPR type max() _NOEXCEPT { return __max; }
@@ -250,10 +239,8 @@ protected:
   static _LIBCPP_CONSTEXPR const int digits       = 1;
   static _LIBCPP_CONSTEXPR const int digits10     = 0;
   static _LIBCPP_CONSTEXPR const int max_digits10 = 0;
-  static _LIBCPP_CONSTEXPR const type __min       = false;
-  static _LIBCPP_CONSTEXPR const type __max       = true;
-  [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI static _LIBCPP_CONSTEXPR type min() _NOEXCEPT { return __min; }
-  [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI static _LIBCPP_CONSTEXPR type max() _NOEXCEPT { return __max; }
+  [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI static _LIBCPP_CONSTEXPR type min() _NOEXCEPT { return false; }
+  [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI static _LIBCPP_CONSTEXPR type max() _NOEXCEPT { return true; }
   [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI static _LIBCPP_CONSTEXPR type lowest() _NOEXCEPT { return min(); }
 
   static _LIBCPP_CONSTEXPR const bool is_integer = true;