[LTO] Add test for dllimport visibility fix

Internal testing showed that the change made in commit 62fcfc5 needed
more test coverage. Specifically, the imported function shouldn't be
externally visibile and the whole test needed to be run in regular LTO
mode.

Differential Revision: https://reviews.llvm.org/D148950

llvm/test/LTO/Resolution/X86/protected-def-dllimport.ll

@@ -0,0 +1,31 @@
+; RUN: llvm-as --disable-verify -o %t0.bc %s
+
+; RUN: llvm-lto2 run -r %t0.bc,__imp_f,l \
+; RUN:               -r %t0.bc,g,p \
+; RUN:               -r %t0.bc,main,x \
+; RUN:               -save-temps -o %t1 %t0.bc
+; RUN: llvm-dis %t1.0.0.preopt.bc -o - | FileCheck %s
+source_filename = "test.cpp"
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+@llvm.used = appending global [2 x ptr] [ ptr @main, ptr @f ], section "llvm.metadata"
+
+$g = comdat any
+@g = global i8 42, comdat, !type !0
+
+; CHECK: declare protected ptr @f()
+define protected dllimport i8* @f() {
+  ret i8* @g
+}
+
+define available_externally i32 @main() {
+  %1 = call i8* @f()
+  %2 = ptrtoint i8* %1 to i32
+  ret i32 %2
+}
+
+!llvm.module.flags = !{!1}
+
+!0 = !{i32 0, !"typeid"}
+!1 = !{i32 1, !"ThinLTO", i32 0}