architecture macros (__mips_n64, __powerpc64__) when 64 bit types (and
corresponding macros) are different from 32 bit. [1]
Correct the type of INT64_MIN, INT64_MAX and UINT64_MAX.
Define (U)INTMAX_C as an alias for (U)INT64_C matching the type definition
for (u)intmax_t. Do this on all architectures for consistency.
Suggested by: bde [1]
Approved by: kib (mentor)