Add support for comparisons against integer immediates

* libguile/vm-engine.c (s64-imm=?, u64-imm<?, imm-u64<?, s64-imm<?)
  (imm-s64<?): New instructions.
* libguile/instructions.c (FOR_EACH_INSTRUCTION_WORD_TYPE): Add new
  X8_S12_Z12 word type used by the new S64/immediate instructions.  A
  Z12 is a 12-bit signed integer immediate.
* module/system/vm/assembler.scm: Export new instructions, and add
  X8_S12_Z12 support.  Also, add missing shufflers for X8_S12_C12.
* module/language/bytecode.scm (compute-instruction-arity):
* module/system/vm/disassembler.scm (unpack-s12, disassembler): Add
  support for X8_S12_Z12.
* module/language/cps/types.scm (define-predicate-inferrer/param): New
  helper.
  (u64-=, u64-<, s64-<): Remove type checkers; this procedure does not
  cause &type-check.
  (u64-imm=?, s64-imm=?, u64-imm<?, imm-u64<?, s64-imm<?, imm-s64<?):
  New type inferrers.
* module/language/cps/type-fold.scm (define-unary-branch-folder*): New
  helper.
  (u64-imm=?, s64-imm=?, u64-imm<?, imm-u64<?, s64-imm<?, imm-s64<?):
  New branch folders.
* module/language/cps/reify-primitives.scm (reify-primitives): Reify
  constants for new immediate branching primcalls if values out of
  range.
* module/language/cps/effects-analysis.scm: Add support for new
  primcalls.
* module/language/cps/compile-bytecode.scm (compile-function): Add
  support for new primcalls and instructions.  Compile u64-imm-= to
  s64-imm=?.

module/language/cps/primitives.scm

@@ -139,7 +139,6 @@ before it is lowered to CPS?"
     u64-=
 
     s64-<
-    s64-=
 
     f64-<
     f64-=))