Match:Support IMM=-1 for signed scalar SAT_ADD IMM form1

Match:Support IMM=-1 for signed scalar SAT_ADD IMM form1

This patch would like to support .SAT_ADD when IMM=-1.

Form1:
T __attribute__((noinline))                  \
sat_s_add_imm_##T##_fmt_1##_##INDEX (T x)             \
{                                            \
  T sum = (UT)x + (UT)IMM;                     \
  return (x ^ IMM) < 0                         \
    ? sum                                    \
    : (sum ^ x) >= 0                         \
      ? sum                                  \
      : x < 0 ? MIN : MAX;                   \
}

Take below form1 as example:
DEF_SAT_S_ADD_IMM_FMT_1(0, int8_t, uint8_t, -1, INT8_MIN, INT8_MAX)

Before this patch:
__attribute__((noinline))
int8_t sat_s_add_imm_int8_t_fmt_1_0 (int8_t x)
{
  unsigned char x.0_1;
  unsigned char _2;
  unsigned char _3;
  int8_t iftmp.1_4;
  signed char _8;
  unsigned char _9;
  signed char _10;

  <bb 2> [local count: 1073741824]:
  x.0_1 = (unsigned char) x_5(D);
  _3 = -x.0_1;
  _10 = (signed char) _3;
  _8 = x_5(D) & _10;
  if (_8 < 0)
    goto <bb 4>; [1.40%]
  else
    goto <bb 3>; [98.60%]

  <bb 3> [local count: 434070867]:
  _2 = x.0_1 + 255;

  <bb 4> [local count: 1073741824]:
  # _9 = PHI <_2(3), 128(2)>
  iftmp.1_4 = (int8_t) _9;
  return iftmp.1_4;

}

After this patch:
__attribute__((noinline))
int8_t sat_s_add_imm_int8_t_fmt_1_0 (int8_t x)
{
  int8_t _4;

  <bb 2> [local count: 1073741824]:
  gimple_call <.SAT_ADD, _4, x_5(D), 255> [tail call]
  gimple_return <_4>

}

The below test suites are passed for this patch:
1. The rv64gcv fully regression tests.
2. The x86 bootstrap tests.
3. The x86 fully regression tests.

Signed-off-by: Li Xu <xuli1@eswincomputing.com>
gcc/ChangeLog:

	* match.pd: Add signed scalar SAT_ADD IMM form1 with IMM=-1 matching.
	* tree-ssa-math-opts.cc (match_unsigned_saturation_add): Adapt function name.
	(match_saturation_add_with_assign): Match signed and unsigned SAT_ADD with assign.
	(math_opts_dom_walker::after_dom_children): Match imm=-1 signed SAT_ADD with NOP_EXPR case.