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

[Nick Sarnie via llvm-commits]

================
@@ -2668,6 +2668,11 @@ static void addMBBNames(const Module &M, const SPIRVInstrInfo &TII,
     MachineFunction *MF = MMI->getMachineFunction(F);
     if (!MF)
       continue;
+    if (MF->getFunction()
----------------
sarnex wrote:

I can, but I will need to disable tests because they start failing with other parts of this change and are fixed by this line. Let me know what you prefer. 

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