Make code size metric names independent of platform

[paquette]

Summary

On Darwin/mach-o, llvm-size (and size) will output something like

__text

While on other platforms (e.g. GNU) you'll get

.text

codesize.py was basically pushing that platform-specific info along in its size
related output.

So, depending on the platform, we'd get

size.__text
size..text

Tools downstream from the test suite then would have to handle whatever output
the target-specific tools would produce.

Instead of doing that, let's just output something like

size_text

So all downstream consumers can just handle one single format.

This is in tandem with D146257 in LNT.

[fhahn]

LGTM, thanks!

@cmatthews @azhar do you know if there are any tests for this part of the code?

[paquette]

Over in D146257 we decided that we don't want to change the test suite, and would prefer the change to be local to LNT. We don't need this change.

[azharudd]

@jpaquette, what do you think?

litsupport/modules/codesize.py

42

I was just thinking maybe, as a good measure, we can assert here that only one of size.__text or size..text is present in metrics.

assert not ('size.__text' in metrics and 'size..text' in metrics), "Both 'size.__text' and 'size..text' present in metrics. Only one of them should exist."

[paquette]

litsupport/modules/codesize.py

42

Sure, that sounds like a good idea. Lemme spin up another patch.