[llvm] [SPIRV] Fix global emission for modules with no functions (PR #183833)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `llvm-clang-x86_64-expensive-checks-ubuntu` running on `as-builder-4` while building `llvm` at step 7 "test-check-all".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/187/builds/17475

<details>
<summary>Here is the relevant piece of the build log for the reference</summary>

```
Step 7 (test-check-all) failure: Test just built components: check-all completed (failure)
******************** TEST 'LLVM :: CodeGen/SPIRV/CheckCapKernelWithoutKernel.ll' FAILED ********************
Exit Code: 2

Command Output (stdout):
--
# RUN: at line 1
/home/buildbot/worker/as-builder-4/ramdisk/expensive-checks/build/bin/llc -O0 -mtriple=spirv64-unknown-unknown /home/buildbot/worker/as-builder-4/ramdisk/expensive-checks/llvm-project/llvm/test/CodeGen/SPIRV/CheckCapKernelWithoutKernel.ll -o - | /home/buildbot/worker/as-builder-4/ramdisk/expensive-checks/build/bin/FileCheck /home/buildbot/worker/as-builder-4/ramdisk/expensive-checks/llvm-project/llvm/test/CodeGen/SPIRV/CheckCapKernelWithoutKernel.ll
# executed command: /home/buildbot/worker/as-builder-4/ramdisk/expensive-checks/build/bin/llc -O0 -mtriple=spirv64-unknown-unknown /home/buildbot/worker/as-builder-4/ramdisk/expensive-checks/llvm-project/llvm/test/CodeGen/SPIRV/CheckCapKernelWithoutKernel.ll -o -
# .---command stderr------------
# | llc: /home/buildbot/worker/as-builder-4/ramdisk/expensive-checks/llvm-project/llvm/lib/IR/LegacyPassManager.cpp:1517: bool (anonymous namespace)::MPPassManager::runOnModule(Module &): Assertion `(LocalChanged || (RefHash == MP->structuralHash(M))) && "Pass modifies its input and doesn't report it."' failed.
# | PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace and instructions to reproduce the bug.
# | Stack dump:
# | 0.	Program arguments: /home/buildbot/worker/as-builder-4/ramdisk/expensive-checks/build/bin/llc -O0 -mtriple=spirv64-unknown-unknown /home/buildbot/worker/as-builder-4/ramdisk/expensive-checks/llvm-project/llvm/test/CodeGen/SPIRV/CheckCapKernelWithoutKernel.ll -o -
# | 1.	Running pass 'SPIRV prepare functions' on module '/home/buildbot/worker/as-builder-4/ramdisk/expensive-checks/llvm-project/llvm/test/CodeGen/SPIRV/CheckCapKernelWithoutKernel.ll'.
# |  #0 0x00005d833862a738 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/home/buildbot/worker/as-builder-4/ramdisk/expensive-checks/build/bin/llc+0x86c6738)
# |  #1 0x00005d83386276a5 llvm::sys::RunSignalHandlers() (/home/buildbot/worker/as-builder-4/ramdisk/expensive-checks/build/bin/llc+0x86c36a5)
# |  #2 0x00005d833862b591 SignalHandler(int, siginfo_t*, void*) Signals.cpp:0:0
# |  #3 0x0000734744e45330 (/lib/x86_64-linux-gnu/libc.so.6+0x45330)
# |  #4 0x0000734744e9eb2c pthread_kill (/lib/x86_64-linux-gnu/libc.so.6+0x9eb2c)
# |  #5 0x0000734744e4527e raise (/lib/x86_64-linux-gnu/libc.so.6+0x4527e)
# |  #6 0x0000734744e288ff abort (/lib/x86_64-linux-gnu/libc.so.6+0x288ff)
# |  #7 0x0000734744e2881b (/lib/x86_64-linux-gnu/libc.so.6+0x2881b)
# |  #8 0x0000734744e3b517 (/lib/x86_64-linux-gnu/libc.so.6+0x3b517)
# |  #9 0x00005d833784f62c llvm::legacy::PassManagerImpl::run(llvm::Module&) (/home/buildbot/worker/as-builder-4/ramdisk/expensive-checks/build/bin/llc+0x78eb62c)
# | #10 0x00005d833502ef6f compileModule(char**, llvm::SmallVectorImpl<llvm::PassPlugin>&, llvm::LLVMContext&, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>&) llc.cpp:0:0
# | #11 0x00005d833502c243 main (/home/buildbot/worker/as-builder-4/ramdisk/expensive-checks/build/bin/llc+0x50c8243)
# | #12 0x0000734744e2a1ca (/lib/x86_64-linux-gnu/libc.so.6+0x2a1ca)
# | #13 0x0000734744e2a28b __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x2a28b)
# | #14 0x00005d8335027d65 _start (/home/buildbot/worker/as-builder-4/ramdisk/expensive-checks/build/bin/llc+0x50c3d65)
# `-----------------------------
# error: command failed with exit status: -6
# executed command: /home/buildbot/worker/as-builder-4/ramdisk/expensive-checks/build/bin/FileCheck /home/buildbot/worker/as-builder-4/ramdisk/expensive-checks/llvm-project/llvm/test/CodeGen/SPIRV/CheckCapKernelWithoutKernel.ll
# .---command stderr------------
# | FileCheck error: '<stdin>' is empty.
# | FileCheck command line:  /home/buildbot/worker/as-builder-4/ramdisk/expensive-checks/build/bin/FileCheck /home/buildbot/worker/as-builder-4/ramdisk/expensive-checks/llvm-project/llvm/test/CodeGen/SPIRV/CheckCapKernelWithoutKernel.ll
# `-----------------------------
# error: command failed with exit status: 2

--

********************


```

</details>

https://github.com/llvm/llvm-project/pull/183833