Reland [X86] With large code model, put functions into .ltext with large section flag (#73037)

So that when mixing small and large text, large text stays out of the
way of the rest of the binary.

This is useful for mixing precompiled small code model object files and
built-from-source large code model binaries so that the the text
sections don't get merged.

The reland fixes an issue where a function in the large code model would reference small data without GOTOFF.

This was incorrectly reverted in 76f78ecc.