[lto] Add a useful test case.

This is reduced from an issue found in practice.
The original version of D18012 needed another patch to handle this, but
it now works since we are using a more correct GV->hasAppendingLinkage()
check that Rafael suggested.

This is what remains of that other patch.

llvm-svn: 263181

diff --git a/lld/test/ELF/lto/linkage.ll b/lld/test/ELF/lto/linkage.ll
index f0f4610..ee1c70c 100644 (file)
--- a/lld/test/ELF/lto/linkage.ll
+++ b/lld/test/ELF/lto/linkage.ll
@@ -13,3 +13,6 @@ target triple = "x86_64-unknown-linux-gnu"
 define internal void @ctor() {
   ret void
 }
+
+; Should not try to merge a declaration into the combined module.
+declare i32 @llvm.ctpop.i32(i32)