[Clang] __{,u}INT_FAST{16,32}_TYPE__ is incorrect

The following should work just fine AFAICT:
```
#include

static_assert(__is_same(int8_t, __INT8_TYPE__));
static_assert(__is_same(int16_t, __INT16_TYPE__));
static_assert(__is_same(int32_t, __INT32_TYPE__));
static_assert(__is_same(int64_t, __INT64_TYPE__));
static_assert(__is_same(int_least8_t, __INT_LEAST8_TYPE__));
static_assert(__is_same(int_least16_t, __INT_LEAST16_TYPE__));
static_assert(__is_same(int_least32_t, __INT_LEAST32_TYPE__));
static_assert(__is_same(int_fast64_t, __INT_FAST64_TYPE__));
static_assert(__is_same(int_fast8_t, __INT_FAST8_TYPE__));
static_assert(__is_same(int_fast16_t, __INT_FAST16_TYPE__));
static_assert(__is_same(int_fast32_t, __INT_FAST32_TYPE__));
static_assert(__is_same(int_fast64_t, __INT_FAST64_TYPE__));
static_assert(__is_same(intptr_t, __INTPTR_TYPE__));
static_assert(__is_same(intmax_t, __INTMAX_TYPE__));

static_assert(__is_same(uint8_t, __UINT8_TYPE__));
static_assert(__is_same(uint16_t, __UINT16_TYPE__));
static_assert(__is_same(uint32_t, __UINT32_TYPE__));
static_assert(__is_same(uint64_t, __UINT64_TYPE__));
static_assert(__is_same(uint_least8_t, __UINT_LEAST8_TYPE__));
static_assert(__is_same(uint_least16_t, __UINT_LEAST16_TYPE__));
static_assert(__is_same(uint_least32_t, __UINT_LEAST32_TYPE__));
static_assert(__is_same(uint_least64_t, __UINT_LEAST64_TYPE__));
static_assert(__is_same(uint_fast8_t, __UINT_FAST8_TYPE__));
static_assert(__is_same(uint_fast16_t, __UINT_FAST16_TYPE__));
static_assert(__is_same(uint_fast32_t, __UINT_FAST32_TYPE__));
static_assert(__is_same(uint_fast64_t, __UINT_FAST64_TYPE__));
static_assert(__is_same(uintptr_t, __UINTPTR_TYPE__));
static_assert(__is_same(uintmax_t, __UINTMAX_TYPE__));
```
However, at least with glibc, a few of the `static_assert`s currently fail. Note that with GCC this does in fact work: https://godbolt.org/z/xjcGzq4Mb

Start by compiling the reproducer from the issue with Clang and glibc, then compare its failing assertions with GCC using the linked Compiler Explorer example. Trace how Clang defines the __INT_FAST and __UINT_FAST type macros and make the listed static_assert checks pass without breaking the other integer type macros.

Written by the indexing model from the issue text.