[Issue 23483] add profile-gc hook function user can call early to dump partial report file.

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=23483

--- Comment #2 from mw <mingwu at gmail.com> ---
The nice thing about valgrind is that even if the program segfaults, it can
still generate the report file.

profile-gc should have this behavior, instead of insisting on program exit
normally.

To debug a out-of-memory problem, you have to terminate the program early,
often abnormally.

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