Bug 1914501 - Don't run emerge when all packages have been filtered out....

Bug 1914501 - Don't run emerge when all packages have been filtered out. r=firefox-build-system-reviewers,sergesanspaille a=npotb

Differential Revision: https://phabricator.services.mozilla.com/D220203

python/mozboot/mozboot/gentoo.py

@@ -20,7 +20,8 @@ class GentooBootstrapper(LinuxBootstrapper, BaseBootstrapper):
         }
         # watchman is available but requires messing with USEs.
         packages = [DISAMBIGUATE.get(p, p) for p in packages if p != "watchman"]
-        self.run_as_root(["emerge", "--noreplace"] + packages)
+        if packages:
+            self.run_as_root(["emerge", "--noreplace"] + packages)
 
     def _update_package_manager(self):
         self.run_as_root(["emerge", "--sync"])