Fix incorrect caching of Julia-LLVM type mapping with llvmcall (#34109)

Author: thomasfaingnaert

src/cgutils.cpp

@@ -693,7 +693,9 @@ static Type *julia_struct_to_llvm(jl_value_t *jt, jl_unionall_t *ua, bool *isbox
 #endif
                 decl = StructType::get(jl_LLVMContext, latypes);
             }
-            jst->struct_decl = decl;
+            // don't use struct_decl cache for llvmcall
+            if (!llvmcall)
+                jst->struct_decl = decl;
             return decl;
         }
     }

test/llvmpasses/llvmcall.jl

@@ -6,6 +6,7 @@
 include(joinpath("..", "testhelpers", "llvmpasses.jl"))
 
 @generated foo(x)=:(ccall("extern foo", llvmcall, $x, ($x,), x))
+bar(x) = ntuple(i -> VecElement{Float16}(x[i]), 2)
 
 # CHECK: call half @foo(half zeroext %{{[0-9]+}})
 emit(foo, Float16)
@@ -15,3 +16,6 @@ emit(foo, NTuple{2, Float16})
 
 # CHECK: call <2 x half> @foo(<2 x half> %{{[0-9]+}})
 emit(foo, NTuple{2, VecElement{Float16}})
+
+# CHECK: define <2 x i16> @julia_bar_{{[0-9]+}}([2 x i16]
+emit(bar, NTuple{2, Float16})