[lilliput-jdk17u:lilliput] RFR: 8308172: [Lilliput/JDK17] Revert disabling vzeroupper

[Roman Kennke]

While looking through the diff between Lilliput/JDK17 and upstream JDK17, I noticed one change in library_call.cpp that should not be there, it probably slipped through from debugging.

        void clear_upper_avx() {
      #ifdef X86
    -     if (UseAVX >= 2) {
    +     if (false && UseAVX >= 2) {
            C->set_clear_upper_avx(true);
          }
      #endif
        }
 
This prevents emitting vzeroupper instructions on x86_64. I believe this will have performance impact when transitioning between AVX and SSE code. We should revert this.

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Commit messages:
 - 8308172: [Lilliput/JDK17] Revert disabling vzeroupper

Changes: https://git.openjdk.org/lilliput-jdk17u/pull/18/files
 Webrev: https://webrevs.openjdk.org/?repo=lilliput-jdk17u&pr=18&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8308172
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/lilliput-jdk17u/pull/18.diff
  Fetch: git fetch https://git.openjdk.org/lilliput-jdk17u.git pull/18/head:pull/18

PR: https://git.openjdk.org/lilliput-jdk17u/pull/18