Fix reachable_set for non-function items in non-library crates

[ghost]

I unintentionally changed reachable_set to ignore non-function items when !self.any_library in #86492, which can lead to "undefined reference" errors to symbols in non-library (cdylib/staticlib/bin) crates, for example: https://play.rust-lang.org/?version=nightly&mode=debug&edition=2018&gist=6bb2c5065a9be7e40943d0541e161b5a

This PR restores the behavior of reachable_set for non-function items.

Fixes #88016.

The modified test will fail with this output without the reachable_set change

---- [codegen] codegen/external-no-mangle-statics.rs#staticlib stdout ----

error in revision `staticlib`: verification with 'FileCheck' failed
status: exit status: 1
command: "/checkout/build/x86_64-unknown-linux-gnu/ci-llvm/bin/FileCheck" "--input-file" "/checkout/build/x86_64-unknown-linux-gnu/test/codegen/external-no-mangle-statics.staticlib/external-no-mangle-statics.ll" "/checkout/src/test/codegen/external-no-mangle-statics.rs" "--check-prefixes" "CHECK,NONMSVC,staticlib"
stdout:
------------------------------------------

------------------------------------------
stderr:
------------------------------------------
/checkout/src/test/codegen/external-no-mangle-statics.rs:10:11: error: CHECK: expected string not found in input
// CHECK: @A = local_unnamed_addr constant
          ^
/checkout/build/x86_64-unknown-linux-gnu/test/codegen/external-no-mangle-statics.staticlib/external-no-mangle-statics.ll:1:1: note: scanning from here
; ModuleID = 'external_no_mangle_statics.b50529d3-cgu.0'
^
/checkout/build/x86_64-unknown-linux-gnu/test/codegen/external-no-mangle-statics.staticlib/external-no-mangle-statics.ll:1:6: note: possible intended match here
; ModuleID = 'external_no_mangle_statics.b50529d3-cgu.0'
     ^

Input file: /checkout/build/x86_64-unknown-linux-gnu/test/codegen/external-no-mangle-statics.staticlib/external-no-mangle-statics.ll
Check file: /checkout/src/test/codegen/external-no-mangle-statics.rs

-dump-input=help explains the following input dump.

Input was:
<<<<<<
            1: ; ModuleID = 'external_no_mangle_statics.b50529d3-cgu.0'
check:10'0     X~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ error: no match found
check:10'1          ?                                                   possible intended match
            2: source_filename = "external_no_mangle_statics.b50529d3-cgu.0"
check:10'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
            3: target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
check:10'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
            4: target triple = "x86_64-unknown-linux-gnu"
check:10'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
            5:
check:10'0     ~
            6: !llvm.module.flags = !{!0, !1}
check:10'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
            .
            .
            .
>>>>>>

------------------------------------------

failures:
    [codegen] codegen/external-no-mangle-statics.rs#staticlib