Add FreeBSD platforms' build.

[chirontt]

• part of eclipse-platform/eclipse.platform.releng.aggregator#2959
• add 2 file system modules for FreeBSD: org.eclipse.core.filesystem.freebsd.aarch64 and org.eclipse.core.filesystem.freebsd.x86_64
• add a Makefile to compile the file system natives for FreeBSD.

To support cross-compiling from Linux to FreeBSD, for the same hardware architecture, a Docker container is made available in my fork with detailed instructions: https://github.com/chirontt/eclipse.platform.releng.aggregator/tree/master/cje-production/dockerfiles/alpine/freebsd-cross which will be submitted to the official repo at later stage.

[github-actions[bot]]

Test Results

0 files   -  1 758  0 suites   - 1 758   0s ⏱️ - 1h 28m 55s 0 tests  -  4 173  0 ✅  -  4 150  0 💤  -  23  0 ❌ ±0  0 runs   - 13 119  0 ✅  - 12 952  0 💤  - 167  0 ❌ ±0 

Results for commit eedb74d2. ± Comparison against base commit e16edfe4.

[chirontt]

Closing as there isn't a viable path forward for FreeBSD.