[LLD] [COFF] [test] Readd lto-late-arm.ll (#143494)

This testcase was removed in 4cafd28b7d,
as a082f665f8 had made it no longer
trigger the error that it was supposed to do. (Because the latter of
those two commits makes the symbol "__rt_sdiv" be included among the
potential libcalls listed by lto::LTO::getRuntimeLibcallSymbols().)

Readd the test as a positive test, making sure that such libcalls can
get linked.

We do have preexisting test coverage for LTO libcalls overall in
libcall-archive.ll, but readd this test to cover specifically the ARM
division helper functions as well.

lld/test/COFF/lto-late-arm.ll

@@ -0,0 +1,38 @@
+; REQUIRES: arm
+
+;; A bitcode file can generate undefined references to symbols that weren't
+;; listed as undefined on the bitcode file itself, when lowering produces
+;; calls to e.g. builtin helper functions. Ideally all those functions are
+;; listed by lto::LTO::getRuntimeLibcallSymbols(), then we successfully
+;; can link cases when the helper functions are provided as bitcode too.
+;; (In practice, compiler-rt builtins are always compiled with -fno-lto, so
+;; this shouldn't really happen anyway.)
+
+; RUN: rm -rf %t.dir
+; RUN: split-file %s %t.dir
+; RUN: llvm-as %t.dir/main.ll -o %t.main.obj
+; RUN: llvm-as %t.dir/sdiv.ll -o %t.sdiv.obj
+; RUN: llvm-ar rcs %t.sdiv.lib %t.sdiv.obj
+
+; RUN: lld-link /entry:entry %t.main.obj %t.sdiv.lib /out:%t.exe /subsystem:console
+
+;--- main.ll
+target datalayout = "e-m:w-p:32:32-Fi8-i64:64-v128:64:128-a:0:32-n32-S64"
+target triple = "thumbv7-w64-windows-gnu"
+
+@num = dso_local global i32 100
+
+define dso_local arm_aapcs_vfpcc i32 @entry(i32 %param) {
+entry:
+  %0 = load i32, ptr @num
+  %div = sdiv i32 %0, %param
+  ret i32 %div
+}
+;--- sdiv.ll
+target datalayout = "e-m:w-p:32:32-Fi8-i64:64-v128:64:128-a:0:32-n32-S64"
+target triple = "thumbv7-w64-windows-gnu"
+
+define dso_local arm_aapcs_vfpcc void @__rt_sdiv() {
+entry:
+  ret void
+}