[libc++][modules] Tweak a few includes (#107467)

Add a few missing includes, remove two unnecessary ones and use
__cstddef/size_t.h instead of <cstddef> in a few places. This is a
collection of miscellaneous findings that collectively unblock other
modularization patches.

libcxx/include/__math/copysign.h

@@ -13,7 +13,6 @@
 #include <__type_traits/enable_if.h>
 #include <__type_traits/is_arithmetic.h>
 #include <__type_traits/promote.h>
-#include <limits>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header

libcxx/include/__math/remainder.h

@@ -14,7 +14,6 @@
 #include <__type_traits/is_arithmetic.h>
 #include <__type_traits/is_same.h>
 #include <__type_traits/promote.h>
-#include <limits>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header

libcxx/include/__tuple/find_index.h

@@ -10,8 +10,8 @@
 #define _LIBCPP___TUPLE_FIND_INDEX_H
 
 #include <__config>
+#include <__cstddef/size_t.h>
 #include <__type_traits/is_same.h>
-#include <cstddef>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header

libcxx/include/__tuple/make_tuple_types.h

@@ -10,6 +10,7 @@
 #define _LIBCPP___TUPLE_MAKE_TUPLE_TYPES_H
 
 #include <__config>
+#include <__cstddef/size_t.h>
 #include <__fwd/array.h>
 #include <__fwd/tuple.h>
 #include <__tuple/tuple_element.h>
@@ -19,7 +20,6 @@
 #include <__type_traits/copy_cvref.h>
 #include <__type_traits/remove_cv.h>
 #include <__type_traits/remove_reference.h>
-#include <cstddef>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header

libcxx/include/__tuple/sfinae_helpers.h

@@ -10,6 +10,7 @@
 #define _LIBCPP___TUPLE_SFINAE_HELPERS_H
 
 #include <__config>
+#include <__cstddef/size_t.h>
 #include <__fwd/tuple.h>
 #include <__tuple/make_tuple_types.h>
 #include <__tuple/tuple_element.h>
@@ -23,7 +24,6 @@
 #include <__type_traits/is_same.h>
 #include <__type_traits/remove_cvref.h>
 #include <__type_traits/remove_reference.h>
-#include <cstddef>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header

libcxx/include/__tuple/tuple_element.h

@@ -10,9 +10,9 @@
 #define _LIBCPP___TUPLE_TUPLE_ELEMENT_H
 
 #include <__config>
+#include <__cstddef/size_t.h>
 #include <__tuple/tuple_indices.h>
 #include <__tuple/tuple_types.h>
-#include <cstddef>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header

libcxx/include/__tuple/tuple_indices.h

@@ -10,8 +10,8 @@
 #define _LIBCPP___TUPLE_MAKE_TUPLE_INDICES_H
 
 #include <__config>
+#include <__cstddef/size_t.h>
 #include <__utility/integer_sequence.h>
-#include <cstddef>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header

libcxx/include/__tuple/tuple_like_ext.h

@@ -10,12 +10,12 @@
 #define _LIBCPP___TUPLE_TUPLE_LIKE_EXT_H
 
 #include <__config>
+#include <__cstddef/size_t.h>
 #include <__fwd/array.h>
 #include <__fwd/pair.h>
 #include <__fwd/tuple.h>
 #include <__tuple/tuple_types.h>
 #include <__type_traits/integral_constant.h>
-#include <cstddef>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header

libcxx/include/__tuple/tuple_like_no_subrange.h

@@ -10,13 +10,13 @@
 #define _LIBCPP___TUPLE_TUPLE_LIKE_NO_SUBRANGE_H
 
 #include <__config>
+#include <__cstddef/size_t.h>
 #include <__fwd/array.h>
 #include <__fwd/complex.h>
 #include <__fwd/pair.h>
 #include <__fwd/tuple.h>
 #include <__tuple/tuple_size.h>
 #include <__type_traits/remove_cvref.h>
-#include <cstddef>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header

libcxx/include/__tuple/tuple_size.h

@@ -10,13 +10,13 @@
 #define _LIBCPP___TUPLE_TUPLE_SIZE_H
 
 #include <__config>
+#include <__cstddef/size_t.h>
 #include <__fwd/tuple.h>
 #include <__tuple/tuple_types.h>
 #include <__type_traits/enable_if.h>
 #include <__type_traits/integral_constant.h>
 #include <__type_traits/is_const.h>
 #include <__type_traits/is_volatile.h>
-#include <cstddef>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header

libcxx/include/future

@@ -369,6 +369,7 @@ template <class R, class Alloc> struct uses_allocator<packaged_task<R>, Alloc>;
 #  include <__assert>
 #  include <__chrono/duration.h>
 #  include <__chrono/time_point.h>
+#  include <__condition_variable/condition_variable.h>
 #  include <__exception/exception_ptr.h>
 #  include <__memory/addressof.h>
 #  include <__memory/allocator.h>

libcxx/include/variant

@@ -233,7 +233,9 @@ namespace std {
 #include <__type_traits/conjunction.h>
 #include <__type_traits/dependent_type.h>
 #include <__type_traits/is_array.h>
+#include <__type_traits/is_assignable.h>
 #include <__type_traits/is_constructible.h>
+#include <__type_traits/is_convertible.h>
 #include <__type_traits/is_destructible.h>
 #include <__type_traits/is_nothrow_assignable.h>
 #include <__type_traits/is_nothrow_constructible.h>

libcxx/test/libcxx/transitive_includes/cxx11.csv

@@ -354,11 +354,9 @@ future atomic
 future cerrno
 future chrono
 future cstddef
-future cstdint
 future cstdlib
-future cstring
+future ctime
 future exception
-future initializer_list
 future iosfwd
 future limits
 future mutex
@@ -369,7 +367,6 @@ future string
 future system_error
 future thread
 future type_traits
-future typeinfo
 future version
 initializer_list cstddef
 iomanip istream

libcxx/test/libcxx/transitive_includes/cxx14.csv

@@ -357,11 +357,9 @@ future atomic
 future cerrno
 future chrono
 future cstddef
-future cstdint
 future cstdlib
-future cstring
+future ctime
 future exception
-future initializer_list
 future iosfwd
 future limits
 future mutex
@@ -372,7 +370,6 @@ future string
 future system_error
 future thread
 future type_traits
-future typeinfo
 future version
 initializer_list cstddef
 iomanip istream

libcxx/test/libcxx/transitive_includes/cxx17.csv

@@ -357,11 +357,9 @@ future atomic
 future cerrno
 future chrono
 future cstddef
-future cstdint
 future cstdlib
-future cstring
+future ctime
 future exception
-future initializer_list
 future iosfwd
 future limits
 future mutex
@@ -372,7 +370,6 @@ future string
 future system_error
 future thread
 future type_traits
-future typeinfo
 future version
 initializer_list cstddef
 iomanip istream

libcxx/test/libcxx/transitive_includes/cxx20.csv

@@ -364,11 +364,9 @@ functional version
 future atomic
 future cerrno
 future cstddef
-future cstdint
 future cstdlib
-future cstring
+future ctime
 future exception
-future initializer_list
 future iosfwd
 future limits
 future mutex
@@ -379,7 +377,6 @@ future string
 future system_error
 future thread
 future type_traits
-future typeinfo
 future version
 initializer_list cstddef
 iomanip istream

libcxx/test/libcxx/transitive_includes/cxx23.csv

@@ -238,10 +238,8 @@ functional vector
 functional version
 future cerrno
 future cstddef
-future cstdint
 future cstdlib
-future cstring
-future initializer_list
+future ctime
 future limits
 future mutex
 future new

libcxx/test/libcxx/transitive_includes/cxx26.csv

@@ -238,10 +238,8 @@ functional vector
 functional version
 future cerrno
 future cstddef
-future cstdint
 future cstdlib
-future cstring
-future initializer_list
+future ctime
 future limits
 future mutex
 future new