Let breakpad build with -Wall on OS X and Linux.

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 f2f3d5810e1464c4898ed9508e5c6cb262950644..49c2ee15179c5c6dff8e07f41a20fcb1964bb1c3 100644
--- a/src/common/dwarf/dwarf2reader.cc
+++ b/src/common/dwarf/dwarf2reader.cc
@@ -517,8 +517,10 @@ void CompilationUnit::ProcessDIEs() {
 
 LineInfo::LineInfo(const char* buffer, uint64 buffer_length,
                    ByteReader* reader, LineInfoHandler* handler):
-    handler_(handler), reader_(reader), buffer_(buffer),
-    buffer_length_(buffer_length) {
+    handler_(handler), reader_(reader), buffer_(buffer) {
+#ifndef NDEBUG
+  buffer_length_ = buffer_length;
+#endif
   header_.std_opcode_lengths = NULL;
 }