Match: Support form 1 for scalar signed integer SAT_TRUNC

This patch would like to support the form 1 of the scalar signed
integer SAT_TRUNC.  Aka below example:

Form 1:
  #define DEF_SAT_S_TRUNC_FMT_1(NT, WT, NT_MIN, NT_MAX) \
  NT __attribute__((noinline))                          \
  sat_s_trunc_##WT##_to_##NT##_fmt_1 (WT x)             \
  {                                                     \
    NT trunc = (NT)x;                                   \
    return (WT)NT_MIN <= x && x <= (WT)NT_MAX           \
      ? trunc                                           \
      : x < 0 ? NT_MIN : NT_MAX;                        \
  }

DEF_SAT_S_TRUNC_FMT_1(int64_t, int32_t, INT32_MIN, INT32_MAX)

Before this patch:
   4   │ __attribute__((noinline))
   5   │ int32_t sat_s_trunc_int64_t_to_int32_t_fmt_1 (int64_t x)
   6   │ {
   7   │   int32_t trunc;
   8   │   unsigned long x.0_1;
   9   │   unsigned long _2;
  10   │   int32_t _3;
  11   │   _Bool _7;
  12   │   int _8;
  13   │   int _9;
  14   │   int _10;
  15   │
  16   │ ;;   basic block 2, loop depth 0
  17   │ ;;    pred:       ENTRY
  18   │   x.0_1 = (unsigned long) x_4(D);
  19   │   _2 = x.0_1 + 2147483648;
  20   │   if (_2 > 4294967295)
  21   │     goto <bb 4>; [50.00%]
  22   │   else
  23   │     goto <bb 3>; [50.00%]
  24   │ ;;    succ:       4
  25   │ ;;                3
  26   │
  27   │ ;;   basic block 3, loop depth 0
  28   │ ;;    pred:       2
  29   │   trunc_5 = (int32_t) x_4(D);
  30   │   goto <bb 5>; [100.00%]
  31   │ ;;    succ:       5
  32   │
  33   │ ;;   basic block 4, loop depth 0
  34   │ ;;    pred:       2
  35   │   _7 = x_4(D) < 0;
  36   │   _8 = (int) _7;
  37   │   _9 = -_8;
  38   │   _10 = _9 ^ 2147483647;
  39   │ ;;    succ:       5
  40   │
  41   │ ;;   basic block 5, loop depth 0
  42   │ ;;    pred:       3
  43   │ ;;                4
  44   │   # _3 = PHI <trunc_5(3), _10(4)>
  45   │   return _3;
  46   │ ;;    succ:       EXIT
  47   │
  48   │ }

After this patch:
   4   │ __attribute__((noinline))
   5   │ int32_t sat_s_trunc_int64_t_to_int32_t_fmt_1 (int64_t x)
   6   │ {
   7   │   int32_t _3;
   8   │
   9   │ ;;   basic block 2, loop depth 0
  10   │ ;;    pred:       ENTRY
  11   │   _3 = .SAT_TRUNC (x_4(D)); [tail call]
  12   │   return _3;
  13   │ ;;    succ:       EXIT
  14   │
  15   │ }

The below test suites are passed for this patch.
* The rv64gcv fully regression test with pr116861-1.c failed.
* The x86 bootstrap test.
* The x86 fully regression test.

The failed pr116861-1.c ice will be fixed in underlying patch, as it
just trigger one existing bug.

gcc/ChangeLog:

	* match.pd: Add case 1 matching pattern for signed SAT_TRUNC.
	* tree-ssa-math-opts.cc (gimple_signed_integer_sat_trunc): Add
	new decl for signed SAT_TRUNC.
	(match_saturation_trunc): Add new func impl to try SAT_TRUNC
	pattern on phi node.
	(math_opts_dom_walker::after_dom_children): Add
	match_saturation_trunc for phi node iteration.

Signed-off-by: Pan Li <pan2.li@intel.com>