[clang] [CIR] Upstream support for function/call calling conventions (PR #181170)

[Sirui Mu via cfe-commits]

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@@ -2638,7 +2634,6 @@ cir::FuncOp CIRGenModule::createRuntimeFunction(cir::FuncType ty,
   if (entry) {
     // TODO(cir): set the attributes of the function.
     assert(!cir::MissingFeatures::setLLVMFunctionFEnvAttributes());
-    assert(!cir::MissingFeatures::opFuncCallingConv());
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Lancern wrote:

We need to set the calling convention of the created runtime function to be the runtime's CC, thus you should not remove this missing feature assert.

https://github.com/llvm/llvm-project/pull/181170