[ELF,LTO] Test calloc defined in a lazy bitcode file for (malloc+memset => calloc) libcall optimization

Similar to https://reviews.llvm.org/D50017: malloc+memset references can
be combined to a calloc reference, which is not explicit in the
referencer's IR symbol table. If calloc is defined in a lazy bitcode
file, we should extract the archive member to satisfy possible
references from LTO generated object files; otherwise (current status,
which will be fixed by #72673), `calloc` as a LazyObject symbol will be
resolved by compileBitcodeFiles generated Undefined, leading to an
incorrectly-extracted Defined symbol without section, which will lower
to an SHN_ABS symbol at address 0.

Author: MaskRay

lld/test/ELF/lto/libcall-archive-calloc.ll

@@ -0,0 +1,57 @@
+; REQUIRES: x86
+;; malloc+memset references can be combined to a calloc reference.
+;; Test that we extract calloc defined in a lazy bitcode file to satisfy
+;; possible references from LTO generated object files.
+
+; RUN: rm -rf %t && split-file %s %t && cd %t
+; RUN: llvm-as a.ll -o a.bc
+; RUN: llvm-as calloc.ll -o calloc.bc
+; RUN: llvm-mc -filetype=obj -triple=x86_64 lib.s -o lib.o
+; RUN: ld.lld -u foo a.bc --start-lib calloc.bc lib.o --end-lib -o t --save-temps
+; RUN: llvm-dis < t.0.4.opt.bc | FileCheck %s
+; RUN: llvm-nm t | FileCheck %s --check-prefix=NM
+
+; CHECK: declare noalias noundef ptr @calloc(i64 noundef, i64 noundef)
+
+; NM-NOT:  {{.}}
+; NM:      {{.*}} T _start
+;; TODO: Currently the symbol is lazy, which lowers to a SHN_ABS symbol at address 0.
+; NM-NEXT: {{.*}} A calloc
+; NM-NEXT: {{.*}} T foo
+; NM-NEXT: {{.*}} T malloc
+; NM-NEXT: {{.*}} T memset
+; NM-NOT:  {{.}}
+
+;--- a.ll
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+define ptr @foo() noinline {
+entry:
+  %call = tail call noalias ptr @malloc(i64 400)
+  tail call void @llvm.memset.p0.i64(ptr %call, i8 0, i64 400, i1 false)
+  ret ptr %call
+}
+
+define void @_start(ptr %a, ptr %b) {
+entry:
+  call ptr @foo()
+  ret void
+}
+
+declare ptr @malloc(i64)
+declare void @llvm.memset.p0.i64(ptr nocapture writeonly, i8, i64, i1 immarg)
+
+;--- calloc.ll
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+define void @calloc(i64, i64) {
+entry:
+  ret void
+}
+
+;--- lib.s
+.globl malloc, memset
+malloc:
+memset: