[DebugInfo] Simplify and speedup .debug_aranges parsing

Parsing .debug_aranges section now takes O(nlogn) operations instead
of O(n^2), where "n" is the number of address ranges. With this change,
the time required to symbolize an address from a random large
Clang-generated binary drops from 165 seconds to 1.5 seconds.

No functionality change.

llvm-svn: 191781