LowerTypeTests: Change a few vtable globals in tests to constants.

It turns out that some of our negative tests were not in fact providing the
test coverage we expected: they were passing because the vtables were failing
an early check that they were constant. Fix this by changing the globals in
these tests to constants.

llvm-svn: 294550
diff --git a/llvm/test/Transforms/WholeProgramDevirt/vcp-no-this.ll b/llvm/test/Transforms/WholeProgramDevirt/vcp-no-this.ll
index c564665..ce76c8e 100644
--- a/llvm/test/Transforms/WholeProgramDevirt/vcp-no-this.ll
+++ b/llvm/test/Transforms/WholeProgramDevirt/vcp-no-this.ll
@@ -3,8 +3,8 @@
 target datalayout = "e-p:64:64"
 target triple = "x86_64-unknown-linux-gnu"
 
-@vt1 = global [1 x i8*] [i8* bitcast (i32 ()* @vf1 to i8*)], !type !0
-@vt2 = global [1 x i8*] [i8* bitcast (i32 ()* @vf2 to i8*)], !type !0
+@vt1 = constant [1 x i8*] [i8* bitcast (i32 ()* @vf1 to i8*)], !type !0
+@vt2 = constant [1 x i8*] [i8* bitcast (i32 ()* @vf2 to i8*)], !type !0
 
 define i32 @vf1() readnone {
   ret i32 1