Make internal/private GVs implicitly dso_local.

While updating clang tests for having clang set dso_local I noticed
that:

- There are *a lot* of tests to update.
- Many of the updates are redundant.

They are redundant because a GV is "obviously dso_local". This patch
starts formalizing that a bit by requiring that internal and private
GVs be dso_local too. Since they all are, we don't have to print
dso_local to the textual representation, making it a bit more compact
and easier to read.

llvm-svn: 322317

test/Bitcode/thinlto-function-summary-refgraph.ll

@@ -50,7 +50,7 @@
 ; a reference to it when reached while earlier analyzing the phi using its
 ; return value:
 ; op0=Y op4=func2
-; CHECK-DAG:    <PERMODULE {{.*}} op0=8 op1=8 {{.*}} op4=0 op5=3/>
+; CHECK-DAG:    <PERMODULE {{.*}} op0=8 op1=72 {{.*}} op4=0 op5=3/>
 ; Function Z contains call to func2, and ensures we don't incorrectly add
 ; a reference to it when reached while analyzing subsequent use of its return
 ; value: