libfaketime exceptions are not passed down the Mozilla build system properly
It seems that not all the commands passed to `FAKETIME_SKIP_CMDS` are passed down the Mozilla build system which leads to legacy/trac#13877 not being fixable. Quoting from the OS X Firefox descriptor:
```
# XXX Order matters as for some reason the env variable has only the first
# command assigned when it comes to the rsync parts in the build process.
```
issue