RFR: Use os::malloc instead of malloc [v2]

[William Kemper]

> This fixes a compiler error with gcc-10.3.0 used by github actions

William Kemper has updated the pull request incrementally with one additional commit since the last revision:

  Update another use of global malloc/free

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

Changes:
  - all: https://git.openjdk.org/shenandoah/pull/155/files
  - new: https://git.openjdk.org/shenandoah/pull/155/files/551d3a0b..f3473846

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=shenandoah&pr=155&range=01
 - incr: https://webrevs.openjdk.org/?repo=shenandoah&pr=155&range=00-01

  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/shenandoah/pull/155.diff
  Fetch: git fetch https://git.openjdk.org/shenandoah pull/155/head:pull/155

PR: https://git.openjdk.org/shenandoah/pull/155