Bug 1610149 - relax SandboxedWasmLibrary assertions in the mozbuild frontend; r=firefox-build-system-reviewers,rstewart

We're going to enable this on Mac, and it won't do to have configure
assert when we actually do so.

Differential Revision: https://phabricator.services.mozilla.com/D62799

--HG--
extra : moz-landing-system : lando

python/mozbuild/mozbuild/frontend/data.py

@@ -682,8 +682,8 @@ class SandboxedWasmLibrary(Library):
         # TODO: WASM sandboxed libraries are in a weird place: they are
         # built in a different way, but they should share some code with
         # SharedLibrary.  This is the minimal configuration needed to work
-        # with Linux, but it would need to be extended for other platforms.
-        assert context.config.substs['OS_TARGET'] == 'Linux'
+        # on the below platforms.
+        assert context.config.substs['OS_TARGET'] in ('Linux', 'Darwin')
 
         self.lib_name = '%s%s%s' % (
             context.config.dll_prefix,