[clang] Add spirv-val compilation step when targeting SPIR-V (PR #188150)

[Finn Plummer via cfe-commits]

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@@ -0,0 +1,26 @@
+// RUN: mkdir -p %t.dir
+// RUN: env PATH="" %clang_dxc -spirv -I test -Tlib_6_3 -Fo %t.dir/a.spv  -### %s 2>&1 | FileCheck %s
+
+// Make sure report warning, and only once.
+// CHECK:spirv-val not found
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inbelic wrote:

nit: may as well include the full errror message

https://github.com/llvm/llvm-project/pull/188150