Update BacktraceOffline for LLVM rebase to r256229.

Bug: http://b/26987366

(cherry picked from commit 19c30e95167e4879c79007d42ea9c32c4eaa8979)

Change-Id: I5e4568292c0b4bbd2daefc0abd3d36c691622eb4
diff --git a/libbacktrace/BacktraceOffline.cpp b/libbacktrace/BacktraceOffline.cpp
index ac14046..dc3ed67 100644
--- a/libbacktrace/BacktraceOffline.cpp
+++ b/libbacktrace/BacktraceOffline.cpp
@@ -564,7 +564,7 @@
   uint64_t eh_frame_vaddr = 0;
   std::vector<uint8_t> eh_frame_data;
 
-  for (auto it = elf->begin_sections(); it != elf->end_sections(); ++it) {
+  for (auto it = elf->section_begin(); it != elf->section_end(); ++it) {
     llvm::ErrorOr<llvm::StringRef> name = elf->getSectionName(&*it);
     if (name) {
       if (name.get() == ".debug_frame") {
@@ -603,7 +603,7 @@
   }
 
   std::vector<ProgramHeader> program_headers;
-  for (auto it = elf->begin_program_headers(); it != elf->end_program_headers(); ++it) {
+  for (auto it = elf->program_header_begin(); it != elf->program_header_end(); ++it) {
     ProgramHeader header;
     header.vaddr = it->p_vaddr;
     header.file_offset = it->p_offset;