[llvm] [SPIR-V] Add SPV_INTEL_joint_matrix extension (PR #118578)

[Dmitry Sidorov via llvm-commits]

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+; RUN: llc -O0 -mtriple=spirv64-unknown-unknown --spirv-ext=+SPV_KHR_cooperative_matrix,+SPV_INTEL_joint_matrix %s -o - | FileCheck %s
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MrSidims wrote:

spirv-val won't understand it as the capabilities and the instructions are not yet propagated to SPIR-V Headers. 

https://github.com/llvm/llvm-project/pull/118578