[clang] [llvm] [PowerPC] Diagnose musttail instead of crash inside backend (PR #93267)

[Matheus Izvekov via cfe-commits]

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@@ -3833,6 +3833,14 @@ def note_cannot_use_trivial_abi_reason : Note<
   "it is polymorphic|"
   "it has a base of a non-trivial class type|it has a virtual base|"
   "it has a __weak field|it has a field of a non-trivial class type}1">;
+def err_ppc_impossible_musttail: Error<
+  "'musttail' attribute for this call is impossible because %select{"
+  "long calls can not be tail called|"
+  "indirect calls can not be tail called|"
+  "external calls can not be tail called}0"
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mizvekov wrote:

Should this perhaps mention this is a target specific restriction?

https://github.com/llvm/llvm-project/pull/93267