flambda-backend: Fix "make bootstrap" and bootstrap (#1991)

* Fix Target_system for arch=none which happens during bootstrap

* make bootstrap

Author: mshinwell

boot/ocamlc

@@ -20,7 +20,7 @@ let architecture () : architecture =
   | "riscv" -> Riscv
   | arch -> Misc.fatal_errorf "Unknown architecture `%s'" arch
 
-let is_64_bit =
+let is_64_bit () =
   match architecture () with
   | X86_64
   | AArch64
@@ -30,7 +30,7 @@ let is_64_bit =
   | IA32
   | ARM -> false
 
-let is_32_bit = not is_64_bit
+let is_32_bit () = not (is_64_bit ())
 
 type derived_system =
   | Linux

boot/ocamllex

@@ -9,9 +9,9 @@ type architecture =
 
 val architecture : unit -> architecture
 
-val is_64_bit : bool
+val is_64_bit : unit -> bool
 
-val is_32_bit : bool
+val is_32_bit : unit -> bool
 
 type derived_system =
   | Linux