Add support for fetching inlining context (stack of source code locations)

by instruction address from DWARF.

Add --inlining flag to llvm-dwarfdump to demonstrate and test this functionality,
so that "llvm-dwarfdump --inlining --address=0x..." now works much like
"addr2line -i 0x...", provided that the binary has debug info
(Clang's -gline-tables-only *is* enough).

llvm-svn: 163128