Fix deb stretch

[clalancette]

There are 2 commits in here:

1. The first one makes it so things should compile properly on Debian Stretch, by force adding a Qt5Widgets dependency.
2. The second one cleans up some build warnings while I was in here.

[jlblancoc]

Brilliant, thanks!!

However, that build error is, I'm afraid, different than this one (which is on my radar, pending to be fixed someday... (sigh) ):

02:23:32 /usr/bin/cc  -g -O2 -fdebug-prefix-map=/tmp/binarydeb/ros-melodic-mrpt-bridge-0.1.22=. -fstack-protector-strong -Wformat -Werror=format-security -Wdate-time -D_FORTIFY_SOURCE=2     CMakeFiles/cmTC_01feb.dir/CheckSymbolExists.c.o  -o cmTC_01feb -rdynamic 
02:23:32 CMakeFiles/cmTC_01feb.dir/CheckSymbolExists.c.o: In function `main':
02:23:32 ./obj-aarch64-linux-gnu/CMakeFiles/CMakeTmp/CheckSymbolExists.c:8: undefined reference to `pthread_create'
02:23:32 ./obj-aarch64-linux-gnu/CMakeFiles/CMakeTmp/CheckSymbolExists.c:8: undefined reference to `pthread_create'
02:23:32 collect2: error: ld returned 1 exit status

That's an error in the build farm that only happens for Debian, for some reason...

I'm just curious if you succeeded in building the package on Debian without the pthread problem?

Cheers,

[clalancette]

I'm just curious if you succeeded in building the package on Debian without the pthread problem?

I did succeed in building the package. The problem that you see with pthread_create is actually a red herring; the real error is further up in the output. In the link you shared, if you look around 2:23:30, you'll see the real reason for the failure, which this change should fix. I guess we'll find out for sure once we do a new release into Melodic :). Thanks for merging!