[llvm-size][libobject] Add explicit "inTextSegment" methods similar to...

[llvm-size][libobject] Add explicit "inTextSegment" methods similar to "isText" section methods to calculate size correctly.

Summary:
llvm-size uses "isText()" etc. which seem to indicate whether the section contains code-like things, not whether or not it will actually go in the text segment when in a fully linked executable.

The unit test added (elf-sizes.test) shows some types of sections that cause discrepencies versus the GNU size tool. llvm-size is not correctly reporting sizes of things mapping to text/data segments, at least for ELF files.

This fixes pr38723.

Reviewers: echristo, Bigcheese, MaskRay

Reviewed By: MaskRay

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D54369

llvm-svn: 349074