Match:Support signed imm SAT_ADD form1

Match:Support signed imm SAT_ADD form1

This patch would like to support .SAT_ADD when one of the op
is singed IMM.

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, -10, INT8_MIN, INT8_MAX)

Before this patch:
__attribute__((noinline))
int8_t sat_s_add_imm_int8_t_fmt_1_0 (int8_t x)
{
  int8_t sum;
  unsigned char x.0_1;
  unsigned char _2;
  signed char _4;
  int8_t _5;
  _Bool _9;
  signed char _10;
  signed char _11;
  signed char _12;
  signed char _14;
  signed char _16;

  <bb 2> [local count: 1073741824]:
  x.0_1 = (unsigned char) x_6(D);
  _2 = x.0_1 + 246;
  sum_7 = (int8_t) _2;
  _4 = x_6(D) ^ sum_7;
  _16 = x_6(D) ^ 9;
  _14 = _4 & _16;
  if (_14 < 0)
    goto <bb 3>; [41.00%]
  else
    goto <bb 4>; [59.00%]

  <bb 3> [local count: 259738147]:
  _9 = x_6(D) < 0;
  _10 = (signed char) _9;
  _11 = -_10;
  _12 = _11 ^ 127;

  <bb 4> [local count: 1073741824]:
  # _5 = PHI <sum_7(2), _12(3)>
  return _5;

}

After this patch:
__attribute__((noinline))
int8_t sat_s_add_imm_int8_t_fmt_1_0 (int8_t x)
{
  int8_t _5;

  <bb 2> [local count: 1073741824]:
  _5 = .SAT_ADD (x_6(D), -10); [tail call]
  return _5;

}

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 the form1 of signed imm .SAT_ADD matching.
	* tree-ssa-math-opts.cc (match_saturation_add): Add fold
	convert	for const_int to the type of operand 0.