[Bug target/95471] New: vrndvq_f32 not supported on armv8

[evan@coeus-group.com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95471

            Bug ID: 95471
           Summary: vrndvq_f32 not supported on armv8
           Product: gcc
           Version: 9.2.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: evan@coeus-group.com
  Target Milestone: ---

With -march=armv8-a -mfpu=neon, arm_neon.h exposes vrndnq_f32, but the
intrinsic used to implement it (__builtin_neon_vrintnv4sf) emits an "error:
this builtin is not supported for this target".

Here is a trivial test case:

  #include <arm_neon.h>

  #if defined(__ARM_NEON)
  float32x4_t foo(float32x4_t a) {
    return vrndnq_f32(a);
  }
  #endif

On Compiler Explorer: https://godbolt.org/z/ThfJQe

Relevant documentation from ARM:
<https://developer.arm.com/architectures/instruction-sets/simd-isas/neon/intrinsics?search=vrndnq_f32>.