Add more debugging notes on mmap failure.
Add more debugging notes on mmap failure.

Sandboxes and VSS restrictions can cause mmap to fail.  Make that clear when we
crash.

PiperOrigin-RevId: 358502373
Change-Id: Ibf10b113061b7af39561b63920dbacd8abd87e53

google/tcmalloc,google/tcmalloc,google/tcmalloc