[HLSL][SPIRV] Fix calling convention for call in entry function. (#110542)

Fix the calling convention used for the call in the entry point
wrapper. No calling convention is currently set. It can easily use the
calling convention of the function that is being called.

Without this, there is a mismatch in the calling convention between the
call site and the callee. This is undefined behaviour.

Author: s-perron

clang/lib/CodeGen/CGHLSLRuntime.cpp

@@ -415,7 +415,7 @@ void CGHLSLRuntime::emitEntryFunction(const FunctionDecl *FD,
   }
 
   CallInst *CI = B.CreateCall(FunctionCallee(Fn), Args);
-  (void)CI;
+  CI->setCallingConv(Fn->getCallingConv());
   // FIXME: Handle codegen for return type semantics.
   // See: https://github.com/llvm/llvm-project/issues/57875
   B.CreateRetVoid();

clang/test/CodeGenHLSL/semantics/DispatchThreadID.hlsl

@@ -6,7 +6,8 @@
 // CHECK:       define void @foo()
 // CHECK-DXIL:  %[[#ID:]] = call i32 @llvm.[[TARGET]].thread.id(i32 0)
 // CHECK-SPIRV: %[[#ID:]] = call i32 @llvm.[[TARGET]].thread.id(i32 0)
-// CHECK:       call void @{{.*}}foo{{.*}}(i32 %[[#ID]])
+// CHECK-DXIL:       call void @{{.*}}foo{{.*}}(i32 %[[#ID]])
+// CHECK-SPIRV:      call spir_func void @{{.*}}foo{{.*}}(i32 %[[#ID]])
 [shader("compute")]
 [numthreads(8,8,1)]
 void foo(uint Idx : SV_DispatchThreadID) {}
@@ -17,6 +18,7 @@ void foo(uint Idx : SV_DispatchThreadID) {}
 // CHECK:       %[[#ID_Y:]] = call i32 @llvm.[[TARGET]].thread.id(i32 1)
 // CHECK:       %[[#ID_XY:]] = insertelement <2 x i32> %[[#ID_X_]], i32 %[[#ID_Y]], i64 1
 // CHECK-DXIL:  call void @{{.*}}bar{{.*}}(<2 x i32> %[[#ID_XY]])
+// CHECK-SPIRV:  call spir_func void @{{.*}}bar{{.*}}(<2 x i32> %[[#ID_XY]])
 [shader("compute")]
 [numthreads(8,8,1)]
 void bar(uint2 Idx : SV_DispatchThreadID) {}