Debug info: (Bugfix) Make sure artificial functions like _GLOBAL__I_a
are not associated with any source lines.

Previously, if the Location of a Decl was empty, EmitFunctionStart would
just keep using CurLoc, which would sometimes be correct (e.g., thunks)
but in other cases would just point to a hilariously random location.

This patch fixes this by completely eliminating all uses of CurLoc from
EmitFunctionStart and rather have clients explicitly pass in a
SourceLocation for the function header and the function body.

rdar://problem/14985269

llvm-svn: 205999
diff --git a/clang/lib/CodeGen/CGVTables.cpp b/clang/lib/CodeGen/CGVTables.cpp
index 0ad765c..08537d5 100644
--- a/clang/lib/CodeGen/CGVTables.cpp
+++ b/clang/lib/CodeGen/CGVTables.cpp
@@ -217,7 +217,7 @@
 
   // Start defining the function.
   StartFunction(GlobalDecl(), ResultType, Fn, FnInfo, FunctionArgs,
-                SourceLocation());
+                MD->getLocation(), SourceLocation());
 
   // Since we didn't pass a GlobalDecl to StartFunction, do this ourselves.
   CGM.getCXXABI().EmitInstanceFunctionProlog(*this);