Tweak Memcheck sanity tests to avoid duplicate reports.

base/tools_sanity_unittest.cc

Index: base/tools_sanity_unittest.cc
===================================================================
--- base/tools_sanity_unittest.cc	(revision 137375)
+++ base/tools_sanity_unittest.cc	(working copy)
@@ -28,10 +28,10 @@
 #endif
 
 void ReadUninitializedValue(char *ptr) {
-  // The || in the conditional is to prevent clang from optimizing away the
+  // Comparison with 64 is to prevent clang from optimizing away the
   // jump -- valgrind only catches jumps and conditional moves, but clang uses
   // the borrow flag if the condition is just `*ptr == '\0'`.
-  if (*ptr == '\0' || *ptr == 64) {
+  if (*ptr == 64) {
     (*ptr)++;
   } else {
     (*ptr)--;