Revert "Revert "DI: LLVM schema change: fold constants into string""

This reverts commit r218917, effectively reapplying r218913.  Original
commit message follows.

--

Update debug info testcases for an LLVM metadata schema change to fold
metadata constant operands into a single `MDString`.

Part of PR17891.

llvm-svn: 219011
diff --git a/clang/test/CodeGen/2010-02-15-DbgStaticVar.c b/clang/test/CodeGen/2010-02-15-DbgStaticVar.c
index facd14e..a75ffbb 100644
--- a/clang/test/CodeGen/2010-02-15-DbgStaticVar.c
+++ b/clang/test/CodeGen/2010-02-15-DbgStaticVar.c
@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 -g -emit-llvm %s -o - | grep "metadata ..b., metadata ..b., metadata ...,"
+// RUN: %clang_cc1 -g -emit-llvm %s -o - | FileCheck %s
 // Test to check intentionally empty linkage name for a static variable.
 // Radar 7651244.
 static int foo(int a)
@@ -11,3 +11,4 @@
 	int j = foo(1);
 	return 0;
 }
+// CHECK: metadata !"0x34\00b\00b\00\00{{.*}}",