[Inliner] Discard empty COMDAT groups

COMDAT groups which have become rendered unused because of inline are
discardable if we can prove that we've made the group empty.

This fixes PR22285.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@236539 91177308-0d34-0410-b5e6-96231b3b80d8

test/Transforms/Inline/pr22285.ll

@@ -0,0 +1,15 @@
+; RUN: opt < %s -inline -S | FileCheck %s
+
+$f1 = comdat any
+; CHECK-NOT: $f1 = comdat any
+
+define void @f2() {
+  call void @f1()
+  ret void
+}
+; CHECK-LABEL: define void @f2
+
+define linkonce_odr void @f1() comdat {
+  ret void
+}
+; CHECK-NOT: define linkonce_odr void @f1() comdat