This is a C library that it can be used by C++ programs as well.
So the library header will be included in some C++ program and g++
will rise warnings like this:

------
fmcadc-lib.h: In function 'int fmcadc_mshot_buf_max_size_get(fmcadc_dev*, int*)':
fmcadc-lib.h:202:74: warning: deprecated conversion from string constant to 'char*'
[-Wwrite-strings]
         return fmcadc_get_param(dev, "cset0/max-sample-mshot", NULL, value);
------

This patch will suppress all these warning because what we are doing is
correct. The message says that it's deprecated; probably at some point
in time it will not be supported at all and we will see errors instead
of warnings. This patch is suppressing only the warnings.

For the time being we prefer this solution instead of casting strings
to `(char *)` because it's ugly and unclear from C point of view.
Signed-off-by: Federico Vaga <federico.vaga@cern.ch>
Signed-off-by: Juan David Gonzalez Cobas <dcobas@cern.ch>