Let the map function compute the relative pc.

The new packed relocations linker option creates an elf with a non-zero
load base. It's no longer an easy task to compute the relative pc yourself
so call the helper function to do it for us.

Bug: 20687795
Change-Id: If11c1a596bc79382d44e35a86d5035ab29d29864
diff --git a/runtime/utils.cc b/runtime/utils.cc
index ec7131d..e18af00 100644
--- a/runtime/utils.cc
+++ b/runtime/utils.cc
@@ -1298,7 +1298,7 @@
     if (!BacktraceMap::IsValid(it->map)) {
       os << StringPrintf("%08" PRIxPTR "  ???", it->pc);
     } else {
-      os << StringPrintf("%08" PRIxPTR "  ", it->pc - it->map.start);
+      os << StringPrintf("%08" PRIxPTR "  ", BacktraceMap::GetRelativePc(it->map, it->pc));
       os << it->map.name;
       os << " (";
       if (!it->func_name.empty()) {