[Issue 18053] Use stdint.h mangling for int64_t/uint64_t when mangling D long/ulong

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=18053

--- Comment #2 from Walter Bright <bugzilla at digitalmars.com> ---
Only OSX64 changes with this change (from 'm' to 'y').

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