Use exact vector capacities to store DWARF line tables

[sque]

Summary

A large binary's DWARF info can contain line tables with thousands of entries. Since dynamically resized vectors don't have exact capacities, there could be a large amount of wasted space. This patch changes the DWARF reader to store the line table rows in vectors with exact capacities.

lib/DebugInfo/DWARF/DWARFDebugLine.cpp

if (!Sequences.empty()) {
     // Note: actually, instruction address ranges of sequences should not
     // overlap (in shared objects and executables). If they do, the address
     // lookup would still work, though, but result would be ambiguous.
     // We don't report warning in this case. For example,
     // sometimes .so compiled from multiple object files contains a few
     // rudimentary sequences for address ranges [0x0, 0xsomething).
   }
 
+  // There could be hundreds or thousands of Rows in the line table. The vector
+  // will likely have an internal reserved memory block that is much bigger
+  // than necessary. Reduce the reserved capacity to conserve memroy.
+  Rows.shrink_to_fit();
+
   return end_offset;
 }
 
 uint32_t
 DWARFDebugLine::LineTable::findRowInSeq(const DWARFDebugLine::Sequence &seq,
                                         uint64_t address) const {
   if (!seq.containsPC(address))
     return UnknownRowIndex;