package/usbguard: disable on musl

package/usbguard: disable on musl

usbguard doesn't build on musl because it uses GNU version of strerror_r
as well as basename resulting in the following build failure:

In file included from ./src/Library/public/usbguard/Rule.hpp:24,
                 from src/CLI/usbguard-rule-parser.cpp:23:
./src/Library/public/usbguard/Exception.hpp: In static member function 'static std::string usbguard::ErrnoException::reasonFromErrno(int)':
./src/Library/public/usbguard/Exception.hpp:129:72: error: no matching function for call to 'std::__cxx11::basic_string<char>::basic_string(int)'
  129 |       return std::string(strerror_r(errno_value, buffer, sizeof buffer));
      |

Fixes:
 - http://autobuild.buildroot.org/results/ac1fd7b8c7bd65c73a9213a40c5ed1c39204dab0

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>