[clang] [HIP] Define `_OPENMP` on the device for mixed OpenMP CPU compilations (PR #176791)

[Johannes Doerfert via cfe-commits]

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@@ -223,6 +223,7 @@ LANGOPT(NativeInt16Type   , 1, 1, NotCompatible, "Native int 16 type support")
 LANGOPT(CUDA              , 1, 0, NotCompatible, "CUDA")
 LANGOPT(HIP               , 1, 0, NotCompatible, "HIP")
 LANGOPT(OpenMP            , 32, 0, NotCompatible, "OpenMP support and version of OpenMP (31, 40 or 45)")
+LANGOPT(OpenMPMacros      , 1, 0, NotCompatible, "Define the OpenMP Macros")
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jdoerfert wrote:

`m`acro
We should name it "macro(s) only", I think. This would imply it's not (full) OpenMP.

https://github.com/llvm/llvm-project/pull/176791