[PATCH] [RFC] Print exact source locations of global variables in ASan error reports.

[Kostya Serebryany]

seems reasonable, now let's see the tests. 

+glider, who is looking around the same parts of code currently.

================
Comment at: lib/Transforms/Instrumentation/AddressSanitizer.cpp:247
@@ +246,3 @@
+          GlobalVariable *GVLoc = cast<GlobalVariable>(Loc);
+          SourceLocation[GV] = GVLoc;
+          addSourceLocationGlobal(GVLoc);
----------------
can this be done with a single lookup to SourceLocation and only if DN->getOperand(1) is non-zero?

http://reviews.llvm.org/D4203