handle duplicate google_malloc frames in malloc hook stack trace
handle duplicate google_malloc frames in malloc hook stack trace

Subsequent optimization may cause multiple malloc functions in
google_malloc section to be in call stack. Particularly when fast-path
malloc function calls slow-path and compiler chooses to implement such
call as regular call instead of tail-call.

Because we need stacktrace just until first such function, once we find
innermost such frame, we're simply checking if next outer frame is also
google_malloc and consider it instead.

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