Fails to build on macOS Sierra

Sierra includes updates to clock/time support, with the result that the current time shim causes a build error:

```
In file included from /tmp/libgroove-20160925-12053-1ov8e3y/libgroove-4.3.0/grooveplayer/player.c:18:
/tmp/libgroove-20160925-12053-1ov8e3y/libgroove-4.3.0/grooveplayer/osx_time_shim.h:21:13: error: typedef redefinition with different types ('int' vs 'enum clockid_t')
typedef int clockid_t;
^
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.12.sdk/usr/include/time.h:171:3: note: previous definition is here
} clockid_t;
^
1 error generated.
```

Full logs: https://bot.brew.sh/job/Homebrew%20Core%20Pull%20Requests/8242/version=sierra/testReport/junit/brew-test-bot/sierra/install_libgroove/