RFR: 8308407: libjvm library not reproducibly comparable between vendors

[Andrew Leonard]

This PR fixes issue: https://bugs.openjdk.org/browse/JDK-8308407

It ensures that the C compilation of abstract_vm_version.o generates a minimum 64byte static C const for vm_vendor, thus ensuring for most Vendor builds the object has a 64byte string char array.

Since this is just a nul terminated string as before, just within a fixed 64byte location, and should a longer Vendor string be specified it will be longer, there is no change in behavior. It purely provides a fixed 64byte string array in the compiled object, which for most if not all Vendors will be sufficient.

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

Commit messages:
 - 8308407: libjvm library not reproducibly comparable between vendors

Changes: https://git.openjdk.org/jdk/pull/14058/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=14058&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8308407
  Stats: 13 lines in 1 file changed: 8 ins; 4 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/14058.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14058/head:pull/14058

PR: https://git.openjdk.org/jdk/pull/14058