devel/spirv-llvm-translator: update to 20.1.2/19.1.7/18.1.12/1[5-7].0.12

Changes: https://github.com/KhronosGroup/SPIRV-LLVM-Translator/releases/tag/v15.0.12
Changes: https://github.com/KhronosGroup/SPIRV-LLVM-Translator/releases/tag/v16.0.12
Changes: https://github.com/KhronosGroup/SPIRV-LLVM-Translator/releases/tag/v17.0.12
Changes: https://github.com/KhronosGroup/SPIRV-LLVM-Translator/releases/tag/v18.1.12
Changes: https://github.com/KhronosGroup/SPIRV-LLVM-Translator/releases/tag/v19.1.7
Changes: https://github.com/KhronosGroup/SPIRV-LLVM-Translator/releases/tag/v20.1.2
Reported by: GitHub (watch releases)