[master] RFR: JDK-8303823: [Lilliput] Inline initial LockStack stack

[Thomas Stuefe]

Inlines the initial lock stack. This gives us:
- Much higher chance of cache hits when accessing lockstack slots via lockstack header.
- postponed malloc call
- we use actually less memory (not that it matters much) per thread since malloc overhead is at least 48 bytes per allocation, probably more.

Also increases size of initial stack to two slots, and uses realloc instead of malloc+free when growing stack.

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Commit messages:
 - lockstack-inline-initial-stack

Changes: https://git.openjdk.org/lilliput/pull/80/files
 Webrev: https://webrevs.openjdk.org/?repo=lilliput&pr=80&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8303823
  Stats: 16 lines in 2 files changed: 8 ins; 2 del; 6 mod
  Patch: https://git.openjdk.org/lilliput/pull/80.diff
  Fetch: git fetch https://git.openjdk.org/lilliput pull/80/head:pull/80

PR: https://git.openjdk.org/lilliput/pull/80