RFR: 8297491: Loom: Stack chunks allocation code uses TLABs even when TLABs are disabled

[Aleksey Shipilev]

See the bug for more details. The apparent fix it to just test for `UseTLAB` before reaching for TLAB-specific code.

Additional testing:
 - [x] Linux x86_64 fastdebug, `jdk_loom hotspot_loom`
 - [x] Linux x86_64 fastdebug, `jdk_loom hotspot_loom` with `-XX:-UseTLAB` (a single JFR test failure that expects TLAB events, to be fixed separately)

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

Commit messages:
 - Fix

Changes: https://git.openjdk.org/jdk/pull/11317/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=11317&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8297491
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/11317.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11317/head:pull/11317

PR: https://git.openjdk.org/jdk/pull/11317