Fix the macOS build that could fail depending on the SDK. Also, add several basic bmalloc api tests.
Pull request: https://github.com/WebKit/WebKit/pull/275
Committed r292784 (249568@main): <https://commits.webkit.org/249568@main> Reviewed commits have been landed. Closing PR #275 and removing active labels.
<rdar://problem/91648903>