Expect :int_within_limits to fail when ptrdiff_t/*intmax_t differ in base type

The %t{d,u} (ptrdiff_t) tests fail for the following reasons:

• ptrdiff_t is by definition int32_t on !LP64 architectures and int64_t on LP64 architectures.
• intmax_t is by definition fixed to int64_t on all architectures.
• Some of the code in lib/libc/stdio/... is promoting ptrdiff_t to *intmax_t when parsing/representing the value.

PR: 191674
MFC after: 1 week
Sponsored by: Dell EMC Isilon