Infra for mmap memory backed by temporary files

[mpirvu]

This commit adds support for allocating memory using mmap and backing that memory by a temporary file.
The goal is to reduce the amount of physical memory in use by saving the content of an infrequently used memory segment to its backing file using the madvise() system call with a hint of MADV_PAGEOUT.
This feature is only available for Linux.

[mpirvu]

@babsingh Could you please review this portlib PR or delegate? Thanks

[babsingh]

@keithc-ca Can you please review this PR as well?

[mpirvu]

@babsingh I have addressed all your suggestions from the review.
Note that I have added the new trace point at the very end of the tdf file, but that broke the nice grouping by topic that existed in the tdf file.

[mpirvu]

@keithc-ca I have addressed all your comments. The PR is ready for another review. Thanks

[babsingh]

I have addressed all your suggestions from the review.

Thanks.

Note that I have added the new trace point at the very end of the tdf file, but that broke the nice grouping by topic that existed in the tdf file.

Yes, it is a drawback. Currently, we can't preserve the grouping by topic and numbering simultaneously. Preserving tracepoint numbering takes precedence to avoid customer issues.

[keithc-ca]

This looks good, with a suggestion for making it better still.

[babsingh]

jenkins build all

[mpirvu]

The latest push introduces a subtle change: previously, if we failed to open our file, we attempt to use an anonymous map with this code:

		if (OMRPORT_INVALID_FD == fd) {
			/* Revert to using an ANONYMOUS mmap. */
			useBackingSharedTmpFile = FALSE;
			flags = 0;
			useBackingFile = set_flags_for_mmap(&flags);
			Trc_PRT_vmem_reserve_tempfile_not_created(filename, byteAmount);
		}

As long as MAP_ANONYMOUS or MAP_ANON are defined on the system, everything is good. However if MAP_ANONYMOUS and MAP_ANON are not defined, then we try to use a mmap operation with /dev/zero as file and set useBackingFile to TRUE. In this case we need to open that /dev/zero file and have a valid file descriptor, which was not happening. The older code above mine (the one for useBackingSharedFile) had the same flaw.
The change I introduced was to delete an else statement so that we execute the following check again

	if (useBackingFile) {
		fd = portLibrary->file_open(portLibrary, "/dev/zero", EsOpenRead | EsOpenWrite, 0);
	}

[babsingh]

jenkins build all

[babsingh]

jenkins build win

[babsingh]

OSX PR build failed due to a known and unrelated issue: #7181.