[DWARF parser] Refactor fetching DIE address ranges.

Add a helper method to get address ranges specified in a DIE
(either by DW_AT_low_pc/DW_AT_high_pc, or by DW_AT_ranges). Use it
to untangle and simplify the code.

No functionality change.

llvm-svn: 206624
diff --git a/llvm/lib/DebugInfo/DWARFUnit.h b/llvm/lib/DebugInfo/DWARFUnit.h
index 5b4cf09..78997f5 100644
--- a/llvm/lib/DebugInfo/DWARFUnit.h
+++ b/llvm/lib/DebugInfo/DWARFUnit.h
@@ -129,9 +129,7 @@
   const char *getCompilationDir();
   uint64_t getDWOId();
 
-  void buildAddressRangeTable(DWARFDebugAranges *debug_aranges,
-                              bool clear_dies_if_already_not_parsed,
-                              uint32_t CUOffsetInAranges);
+  void collectAddressRanges(DWARFAddressRangesVector &CURanges);
 
   /// getInlinedChainForAddress - fetches inlined chain for a given address.
   /// Returns empty chain if there is no subprogram containing address. The