RFR: 8354473: Incorrect results for compress/expand tests with -XX:+EnableX86ECoreOpts

[Volodymyr Paprotski]

It looks like the `permv` mask isnt always 'all-ones' or 'all-zeroes'. (Which is OK for real blend, but needs to be enforced via the flag for blend emulation)

Before the fix, `make test TEST="jdk/incubator/vector"` (on ECore machine)

==============================
Test summary
==============================
   TEST                                              TOTAL  PASS  FAIL ERROR  SKIP
>> jtreg:test/jdk/jdk/incubator/vector                  83    71    10     0     2 <<
==============================
TEST FAILURE

After the fix:

==============================
Test summary
==============================
   TEST                                              TOTAL  PASS  FAIL ERROR  SKIP
   jtreg:test/jdk/jdk/incubator/vector                  83    81     0     0     2
==============================
TEST SUCCESS

And on an AVX512 machine:

==============================
Test summary
==============================
   TEST                                              TOTAL  PASS  FAIL ERROR  SKIP
   jtreg:test/jdk/jdk/incubator/vector                  83    81     0     0     2
==============================
TEST SUCCESS

-------------

Commit messages:
 - always fixup mask in blend emulation in compress_expand

Changes: https://git.openjdk.org/jdk/pull/24645/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=24645&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8354473
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/24645.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/24645/head:pull/24645

PR: https://git.openjdk.org/jdk/pull/24645