This improves the code generated for float to int64 conversions on x64.
Instead of explicitly checking the input for specific values and
executing conditional jumps, just convert the integer back to a float
and check if this results in the rounded input. The "success value" is
then materialized via vmov + and instead of via branches.

old:
   7  c4e1fb2cd9           vcvttsd2siq rbx,xmm1
   c  ba01000000           movl rdx,0x1
  11  49ba000000000000e0c3 REX.W movq r10,0xc3e0000000000000
  1b  c441f96efa           vmovq xmm15,r10
  20  c5792ef9             vucomisd xmm15,xmm1
  24  7a08                 jpe 0x3599421714ee  <+0x2e>
  26  7408                 jz 0x3599421714f0  <+0x30>
  28  4883fb01             REX.W cmpq rbx,0x1
  2c  7102                 jno 0x3599421714f0  <+0x30>
  2e  33d2                 xorl rdx,rdx

new:
   7  c463010bf90b         vroundsd xmm15,xmm15,xmm1,0xb
   d  c4e1fb2cd9           vcvttsd2siq rbx,xmm1
  12  c4e1832ac3           vcvtqsi2sd xmm0,xmm15,rbx
  17  c4c17bc2c700         vcmpss xmm0,xmm0,xmm15, (eq)
  1d  c4e1f97ec2           vmovq rdx,xmm0
  22  83e201               andl rdx,0x1

A follow-up step would be to replace the explicitly materialized success
value by a direct jump to the code handling the error case, but that
requires more rewrite in TurboFan.

R=tebbi@chromium.org

Bug: v8:10005
Change-Id: Iaedc3f395fb3a8c11c936faa8c6e55c2dfe86cd9
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3560434Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/main@{#79854}