Fixes up dump_syms build on OS X so it works with ELF.

src/common/dwarf/dwarf2reader.cc

Index: src/common/dwarf/dwarf2reader.cc
diff --git a/src/common/dwarf/dwarf2reader.cc b/src/common/dwarf/dwarf2reader.cc
index dc0e2349b02a4a9f07d7d0cf297fa44400247739..a65b43c8a3c0a4c59a74f2f42b1525ddf6ee2905 100644
--- a/src/common/dwarf/dwarf2reader.cc
+++ b/src/common/dwarf/dwarf2reader.cc
@@ -639,7 +639,7 @@ void CompilationUnit::ProcessSplitDwarf() {
     }
   }
   bool found_in_dwp = false;
-  if (dwp_reader_ != NULL) {
+  if (dwp_reader_) {
     // If we have a .dwp file, read the debug sections for the requested CU.
     SectionMap sections;
     dwp_reader_->ReadDebugSectionsForCU(dwo_id_, &sections);