Revert "Promote nameless lambda used by dl_iterate_phdr to named function to...

Revert "Promote nameless lambda used by dl_iterate_phdr to named function to clean up control flow inside findUnwindSections. Also, expose the data structure"

This reverts commit d9337123.

The commit broke the build in several configurations (including
Windows and bare-metal). For details see comments in
https://reviews.llvm.org/D75480