C99 introduced macros of the form `INTn_C(v)` which expand to a signed
or unsigned integer constant with the specified value `v` and the type
`int_leastN_t`. Clang's initial implementation of these macros used
token pasting to form the integer constants, but this means that users
cannot define a macro named `L`, `U`, `UL`, etc before including
`<stdint.h>` (in freestanding mode, where Clang's header is being used)
because that could form invalid token pasting results. The new
definitions now use the predefined `__INTn_C` macros instead of using
token pasting. This matches the behavior of GCC.
Fixes#85995
53f3031005
