Add function signature to code_native and code_llvm

[pchintalapudi]

When getting LLVM IR from @code_llvm, it's sometimes necessary to know exactly which f is being compiled. This prints the type signature of a function in front of code_llvm and code_native to assist in that process.

Example

julia> @code_llvm zeros(64)

; Function Signature: zeros(Int64)
;  @ array.jl:629 within `zeros`
define nonnull {}* @julia_zeros_121(i64 signext %"dims[1]::Int64") #0 {
top:
;  @ array.jl:629 within `zeros` @ array.jl:631 @ array.jl:634
; ┌ @ boot.jl:484 within `Array` @ boot.jl:475
   %0 = call nonnull {}* inttoptr (i64 140604991500960 to {}* ({}*, i64)*)({}* inttoptr (i64 140604630439728 to {}*), i64 %"dims[1]::Int64")
; └
;  @ array.jl:629 within `zeros` @ array.jl:631 @ array.jl:635
; ┌ @ array.jl:392 within `fill!`
; │┌ @ abstractarray.jl:318 within `eachindex`
; ││┌ @ abstractarray.jl:134 within `axes1`
; │││┌ @ abstractarray.jl:98 within `axes`
; ││││┌ @ array.jl:191 within `size`
       %1 = bitcast {}* %0 to { i8*, i64, i16, i16, i32 }*
       %.length_ptr = getelementptr inbounds { i8*, i64, i16, i16, i32 }, { i8*, i64, i16, i16, i32 }* %1, i64 0, i32 1
       %.length = load i64, i64* %.length_ptr, align 8
; │└└└└
; │┌ @ range.jl:897 within `iterate`
; ││┌ @ range.jl:674 within `isempty`
; │││┌ @ operators.jl:378 within `>`
; ││││┌ @ int.jl:83 within `<`
       %.not.not = icmp eq i64 %.length, 0
; │└└└└
   br i1 %.not.not, label %L30, label %L13.preheader

L13.preheader:                                    ; preds = %top
   %2 = bitcast {}* %0 to i8**
   %.data1013 = load i8*, i8** %2, align 8
; │ @ array.jl:394 within `fill!`
   %3 = shl nuw i64 %.length, 3
; │ @ array.jl:393 within `fill!`
; │┌ @ array.jl:1019 within `setindex!`
    call void @llvm.memset.p0i8.i64(i8* nonnull align 8 %.data1013, i8 0, i64 %3, i1 false)
; └└
;  @ array.jl:629 within `zeros`
  br label %L30

L30:                                              ; preds = %L13.preheader, %top
  ret {}* %0
}

[gbaraldi]

I was looking at this and was thinking, should we also print the called functions as well?

[pchintalapudi]

There's probably some things we can do to improve the called function printing, including:

1. Print full signature for when we can deduce the specsig (special cased for already compiled and operating in workqueue)
2. Print the type information for when we can't deduce the specsig, so we fall back to jl_apply_generic