This is a best-effort, least-intrusion attempt to force all of the process's
virtual address space to be loaded before main().  They may later be
*unloaded*, but now main() should begin with all pages loaded into RAM
and in the page table.  Well, of course it's not guaranteed; but it should
work on any reasonable kernel that is not experiencing memory pressure.  And
of course we munlockall() immediately afterward because we don't want to
interfere with the process down the road.

Note that this is *NOT* included in libvmilib.so -- it is only available in
libloadall.so -- we don't want __libc_start_main overridden by default.

I suppose this might not work on some older platforms; don't really know
how long __libc_start_main has been standardized.  Probably a long, long
time.