dl_iterate_phdr is used to search for unwind info provided by either
PT_GNU_EH_FRAME or PT_ARM_EXIDX. Most of the code between the two is
the same, so combine them, and factor out what's different into
- The FrameHeaderCache can now be enabled for ARM EHABI.
- findUnwindSectionsByPhdr now finds the last PT_ARM_EXIDX rather than the first. There should only be one segment.
- The dso_base and text_segment_length fields of UnwindInfoSections are now needed for dl_iterate_phdr when using EHABI, to hold the low and high PC values for a cache entry.