[llvm] [AMDGPU] Fix module split's assumption on kernels (PR #116280)

[Matt Arsenault via llvm-commits]

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@@ -88,7 +88,7 @@ define internal void @HelperC() {
   ret void
 }
 
-define amdgpu_kernel void @C() {
+define weak_odr amdgpu_kernel void @C() {
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arsenm wrote:

Test both cases 

https://github.com/llvm/llvm-project/pull/116280