RISC-V:Bugfix for C++ code compilation failure with rv32imafc_zve32f[pr116883]

RISC-V:Bugfix for C++ code compilation failure with rv32imafc_zve32f[pr116883]

From: xuli <xuli1@eswincomputing.com>

Example as follows:

int main()
{
  unsigned long arraya[128], arrayb[128], arrayc[128];
  for (int i = 0; i < 128; i++)
   {
      arraya[i] = arrayb[i] + arrayc[i];
   }
  return 0;
}

Compiled with -march=rv32imafc_zve32f -mabi=ilp32f, it will cause a compilation issue:

riscv_vector.h:40:25: error: ambiguating new declaration of 'vint64m4_t __riscv_vle64(vbool16_t, const long long int*, unsigned int)'
   40 | #pragma riscv intrinsic "vector"
      |                         ^~~~~~~~
riscv_vector.h:40:25: note: old declaration 'vint64m1_t __riscv_vle64(vbool64_t, const long long int*, unsigned int)'

With zvl=32b, vbool16_t is registered in init_builtins() with
type_common.precision=0x101 (nunits=2), mode_nunits[E_RVVMF16BI]=[2,2].

Normally, vbool64_t is only valid when TARGET_MIN_VLEN > 32, so vbool64_t
is not registered in init_builtins(), meaning vbool64_t=null.

In order to implement __attribute__((target("arch=+v"))), we must register
all vector types and all RVV intrinsics. Therefore, vbool64_t will be registered
by default with zvl=128b in reinit_builtins(), resulting in
type_common.precision=0x101 (nunits=2) and mode_nunits[E_RVVMF64BI]=[2,2].

We then get TYPE_VECTOR_SUBPARTS(vbool16_t) == TYPE_VECTOR_SUBPARTS(vbool64_t),
calculated using type_common.precision, resulting in 2. Since vbool16_t and
vbool64_t have the same element type (boolean_type), the compiler treats them
as the same type, leading to a re-declaration conflict.

After all types and intrinsics have been registered, processing
__attribute__((target("arch=+v"))) will update the parameters option and
init_adjust_machine_modes. Therefore, to avoid conflicts, we can choose
zvl=4096b for the null type reinit_builtins().

command option zvl=32b
  type         nunits
  vbool64_t => null
  vbool32_t=> [1,1]
  vbool16_t=> [2,2]
  vbool8_t=>  [4,4]
  vbool4_t=>  [8,8]
  vbool2_t=>  [16,16]
  vbool1_t=>  [32,32]

reinit zvl=128b
  vbool64_t => [2,2] conflict with zvl32b vbool16_t=> [2,2]
reinit zvl=256b
  vbool64_t => [4,4] conflict with zvl32b vbool8_t=>  [4,4]
reinit zvl=512b
  vbool64_t => [8,8] conflict with zvl32b vbool4_t=>  [8,8]
reinit zvl=1024b
  vbool64_t => [16,16] conflict with zvl32b vbool2_t=>  [16,16]
reinit zvl=2048b
  vbool64_t => [32,32] conflict with zvl32b vbool1_t=>  [32,32]
reinit zvl=4096b
  vbool64_t => [64,64] zvl=4096b is ok

Signed-off-by: xuli <xuli1@eswincomputing.com>
	PR target/116883

gcc/ChangeLog:

	* config/riscv/riscv-c.cc (riscv_pragma_intrinsic_flags_pollute): Choose zvl4096b
	to initialize null type.

gcc/testsuite/ChangeLog:

	* g++.target/riscv/rvv/base/pr116883.C: New test.