[lld/LTO] Test for fix for PR38105

[tejohnson]

Summary

Fix is in LLVM LTO sources (D49138).

Depends on D49138.

test/COFF/Inputs/lto_dllimport.ll

+; ModuleID = 'b.obj'
+source_filename = "b.cpp"
+target datalayout = "e-m:w-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-pc-windows-msvc19.11.0"
+
+; Function Attrs: norecurse nounwind readnone sspstrong uwtable
+define dso_local i32 @"?foo@@YAHXZ"() local_unnamed_addr {
+entry:
+  ret i32 42
+}
+
+!llvm.module.flags = !{!1}
+
+!1 = !{i32 1, !"ThinLTO", i32 0}
+
+^0 = module: (path: "b.obj", hash: (0, 0, 0, 0, 0))
+^1 = gv: (name: "?foo@@YAHXZ", summaries: (function: (module: ^0, flags: (linkage: external, notEligibleToImport: 1, live: 0, dsoLocal: 1), insts: 1, funcFlags: (readNone: 1, readOnly: 0, noRecurse: 1, returnDoesNotAlias: 0)))) ; guid = 2709792123250749187

test/COFF/lto_dllimport.ll

+; Test requiring LTO to remove the __imp_ prefix for locally imported symbols
+; (mirroring how lld handles these symbols).
+; RUN: llvm-as %s -o %t.obj
+; RUN: llvm-as %S/Inputs/lto_dllimport.ll -o %t2.obj
+; RUN: lld-link -entry:main %t.obj %t2.obj /out:%t3.exe
+
+; ModuleID = 'a.obj'
+source_filename = "a.cpp"
+target datalayout = "e-m:w-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-pc-windows-msvc19.11.0"
+
+; Function Attrs: norecurse nounwind sspstrong uwtable
+define dso_local i32 @main() local_unnamed_addr {
+entry:
+  %call = tail call i32 @"?foo@@YAHXZ"()
+  ret i32 %call
+}
+
+declare dllimport i32 @"?foo@@YAHXZ"() local_unnamed_addr
+
+!llvm.module.flags = !{!1}
+
+!1 = !{i32 1, !"ThinLTO", i32 0}
+
+^0 = module: (path: "a.obj", hash: (0, 0, 0, 0, 0))
+^1 = gv: (name: "?foo@@YAHXZ") ; guid = 2709792123250749187
+^2 = gv: (name: "main", summaries: (function: (module: ^0, flags: (linkage: external, notEligibleToImport: 1, live: 0, dsoLocal: 1), insts: 2, funcFlags: (readNone: 0, readOnly: 0, noRecurse: 1, returnDoesNotAlias: 0), calls: ((callee: ^1))))) ; guid = 15822663052811949562