[libclc] Override generic symbol using llvm-link --override flag instead of using weak linkage (#156778) Before this PR, weak linkage is applied to a few CLC generic functions to allow target specific implementation to override generic one. However, adding weak linkage has a side effect of preventing inter-procedural optimization, such as PostOrderFunctionAttrsPass, because weak function doesn't have exact definition (as determined by hasExactDefinition in the pass). This PR resolves the issue by adding --override flag for every non-generic bitcode file in llvm-link run. This approach eliminates the need for weak linkage while still allowing target-specific implementation to override generic one. llvm-diff shows imporoved attribute deduction for some functions in amdgcn--amdhsa.bc, e.g. %23 = tail call half @llvm.sqrt.f16(half %22) => %23 = tail call noundef half @llvm.sqrt.f16(half %22)
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