avoid passing pointers for known Type arguments

[JeffBezanson]

As noticed in #34993.
Before:

julia> code_llvm(*, (Float16,Float16))

;  @ float.jl:398 within `*'
define i16 @"julia_*_66"(i16, i16) {
top:
  %2 = call float @j_Float32_67(%jl_value_t addrspace(10)* addrspacecast (%jl_value_t* inttoptr (i64 140254228698048 to %jl_value_t*) to %jl_value_t addrspace(10)*), i16 %0)
  %3 = call float @j_Float32_68(%jl_value_t addrspace(10)* addrspacecast (%jl_value_t* inttoptr (i64 140254228698048 to %jl_value_t*) to %jl_value_t addrspace(10)*), i16 %1)

After:

julia> code_llvm(*, (Float16,Float16))

;  @ float.jl:398 within `*'
define i16 @"julia_*_70"(i16, i16) {
top:
  %2 = call float @j_Float32_71(i16 %0)
  %3 = call float @j_Float32_72(i16 %1)

[vtjnash]

Should we add a comment that this can be kept in sync with Core.Compiler.hasuniquerep?