[foreign-memaccess+abi] RFR: Add missing include for Linux

[Jorn Vernee]

This PR adds a missing include that is needed on Linux, which didn't show up when compiling under WSL.

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

Commit messages:
 - Add missing include for Linux

Changes: https://git.openjdk.java.net/panama-foreign/pull/614/files
 Webrev: https://webrevs.openjdk.java.net/?repo=panama-foreign&pr=614&range=00
  Stats: 1 line in 1 file changed: 1 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/panama-foreign/pull/614.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-foreign pull/614/head:pull/614

PR: https://git.openjdk.java.net/panama-foreign/pull/614