Fix some warnings

[Holzhaus]

This fixes some of the warnings that popped up while testing my CMake branch with MSVC on Appveyor.

[Be-ing]

Changes to stable branches should only be done to fix bugs that affect real world use of Mixxx. Cleaning code is usually safe, but there is always a risk for regression which is unnecessary on a stable branch. I have retargeted this to master.

[daschuer]

LGTM. Thank you.

[uklotzde]

The GCC build for Xenial build on Travis fails: https://travis-ci.org/mixxxdj/mixxx/jobs/600910492

[MOC] src/preferences/dialog/dlgprefautodj.h

[CXX] lin64_build/src/preferences/dialog/moc_dlgprefautodj.cc

In file included from src/preferences/dialog/dlgprefvinyl.cpp:30:0:

src/preferences/dialog/dlgprefvinyl.cpp: In member function ‘void DlgPrefVinyl::VinylTypeSlotApply()’:

src/util/platform.h:34:32: error: expected primary-expression before ‘__attribute__’

 #define M_FALLTHROUGH_INTENDED __attribute__ ((fallthrough));

                                ^

src/preferences/dialog/dlgprefvinyl.cpp:352:9: note: in expansion of macro ‘M_FALLTHROUGH_INTENDED’

         M_FALLTHROUGH_INTENDED;

         ^

src/util/platform.h:34:32: error: expected primary-expression before ‘__attribute__’

 #define M_FALLTHROUGH_INTENDED __attribute__ ((fallthrough));

                                ^

src/preferences/dialog/dlgprefvinyl.cpp:359:9: note: in expansion of macro ‘M_FALLTHROUGH_INTENDED’

         M_FALLTHROUGH_INTENDED;

         ^

src/util/platform.h:34:32: error: expected primary-expression before ‘__attribute__’

 #define M_FALLTHROUGH_INTENDED __attribute__ ((fallthrough));

                                ^

src/preferences/dialog/dlgprefvinyl.cpp:366:9: note: in expansion of macro ‘M_FALLTHROUGH_INTENDED’

         M_FALLTHROUGH_INTENDED;

         ^

[MOC] src/preferences/dialog/dlgprefbeats.h

scons: *** [lin64_build/src/preferences/dialog/dlgprefvinyl.o] Error 1

scons: building terminated because of errors.

The command "scons $COMMON_FLAGS $EXTRA_FLAGS" failed and exited with 2 during .

Your build has been stopped.

[daschuer]

Ups, I should have notice this before merge, sorry.
Fixed in b83b62d