[dev.link] move FuncID creation into the compiler/assembler

Leaving creation of the funcID till the linker requires the linker to
load the function and file names into memory. Moving these into the
compiler/assembler prevents this.

This work is a step towards moving all func metadata into the compiler.

Change-Id: Iebffdc5a909adbd03ac263fde3f4c3d492fb1eac
Reviewed-on: https://go-review.googlesource.com/c/go/+/244024
Run-TryBot: Jeremy Faller <jeremy@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
Reviewed-by: Austin Clements <austin@google.com>

src/cmd/internal/obj/link.go

@@ -400,6 +400,7 @@ type FuncInfo struct {
 	Args     int32
 	Locals   int32
 	Align    int32
+	FuncID   objabi.FuncID
 	Text     *Prog
 	Autot    map[*LSym]struct{}
 	Pcln     Pcln