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

[Nick Sarnie via llvm-commits]

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@@ -995,7 +995,7 @@ static void processBlockAddr(MachineFunction &MF, SPIRVGlobalRegistry *GR,
 
 static bool isImplicitFallthrough(MachineBasicBlock &MBB) {
   if (MBB.empty())
-    return true;
+    return MBB.getNextNode() != nullptr;
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sarnex wrote:

Same issue as other spot which I replied to seperately, will apply same solution here.

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