[clang] [clang][sema] Suppress unsupported 128-bit mode attribute diagnostic for OpenMP device compilation (PR #214497)

[Mariya Podchishchaeva via cfe-commits]

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+// Host-side compilation on x86 (no errors expected).
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -aux-triple nvptx64 -fopenmp -x c -fsyntax-only -verify=host %s
+
+// Device-side compilation for targets without 128-bit float/complex support (no errors expected).
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Fznamznon wrote:

That highly depends on the CodeGen as well as further lowering and the type itself. The type this PR is poking at doesn't seem to be problematic https://godbolt.org/z/h7515Y3Go though a warning saying please don't do this would probably make sense. 
I remember some types crashed translation from LLVM IR to SPIR-V via the translator tool used in SYCL's downstream so for that purpose `Sema::checkTypeSupport` was invented.

https://github.com/llvm/llvm-project/pull/214497